1. Introduction    

My ultimate goal in this paper is to present a preliminary sketch of the metaphysics of efficient causality propounded by the great Jesuit philosopher and theologian Francisco Suarez (1548-1617) in Disputations 17-19 of his Disputationes Metaphysicae.[1] However, since my motives are systematic rather than historical, I will build up to this presentation gradually by (i) situating my discussion of Aristotelianism in general and of Suarez in particular within the framework of what I take to be the most important currents in contemporary philosophical treatments of causality, causal modality, and scientific explanation, and then by (ii) offering a partial explication and defense of the substance/accident ontology presupposed by Suarez's account of efficient causality. Having done this in sections 2 and 3, I will proceed in section 4 to discuss at some length the notion of per se and immediate efficient causality, which stands at the heart of the account of efficient causality found in section I of Disputation 17, and then to characterize in general terms the distinction between per se and immediate efficient causality on the one hand and more indirect modes of causal contribution on the other. Finally, in the concluding section I will indicate briefly how Suarez develops this basic account of efficient causality in Disputations 18 and 19.  
    

2. Setting the Context    

     2.1 The reemergence of Aristotelianism    

For those of us who think of ourselves as Aristotelians in some broad but substantive sense, the recent history of mainstream Anglo-American philosophy has been, relatively speaking, a joy to behold. Across the board--in metaphysics, epistemology, and ethics--prominent philosophers have articulated and espoused positions that can justifiably be described as Aristotelian, whether or not their authors have always recognized them as such.[2] This is not to say, of course, that the positions in question have gained widespread acceptance. Nonetheless, after decades of what, from an Aristotelian perspective, can only be seen as the regrettable, even if by no means fruitless or uninstructive, domination of Anglo-American philosophy by movements deeply inimical to classical metaphysical traditions, Aristotelianism of various stripes has attained at least a modicum of respectability--something that would have seemed highly improbable only twenty years ago.    

The reemergence of Aristotelianism is nowhere more evident than in those areas of metaphysics that have a special bearing on the philosophy of science. Some recent proponents of scientific realism have argued that properly scientific explanations are those which specify the structures of unified systems or substances along with the causal processes or actions that connect those structures with their characteristic effects--a conception of explanation that is intimately related to Aristotle's notions of formal and efficient causality. Other realists have gone a step further by maintaining that the fundamental general principles of scientific explanation--or 'laws of nature' in at least one of the many uses of that locution--take the form of irreducible ascriptions of basic causal tendencies (or powers or capacities or propensities) to individual systems or substances. These basic causal tendencies are thought of as enduring or, to put it more frankly, essential features possessed by the relevant individuals in virtue of the natural kinds they exemplify--or, to use a less Platonistic and more Aristotelian idiom, in virtue of the intrinsic substantival structures or forms which constitute them as members of natural kinds.[3] Accordingly, the fundamental principles of explanation express de re metaphysical necessities by appeal to which causal modalities such as natural necessity and objective probability are to be analyzed.[4]    

And so it is that 'occult entities', differing only in name, as far as I can tell, from the substantial and accidental forms invoked by medieval Aristotelian philosophy of nature, have found their way back into mainstream discussions of causality, causal modality, and scientific explanation. To be sure, this development has not gone unnoticed or unlamented by those of a more Humean bent who deplore any intimation of 'pre-Kantian metaphysics as practiced after Kant', to use Bas van Fraassen's favorite expression of philosophical disapprobation.[5] As van Fraassen puts it in speaking about explanation:     

Once you decide that explanation is something irreducible and special, the door is opened to elaboration by means of further concepts pertaining thereto, all equally irreducible and special. The premisses of an explanation have to include lawlike statements; a statement is lawlike exactly if it implies some non-trivial counterfactual conditional statement; but it can do so only by asserting relationships of necessity in nature. Not all classes correspond to genuine properties; properties and propensities figure in explanation. Not everyone has joined this return to essentialism or neo-Aristotelian realism, but some eminent realists have publicly explored or advocated it.[6]  

Be that as it may, my present aim is not so much to defend Aristotelianism as to bring it into vivid contrast with its present-day Humean competitors and to identify its key assumptions.  
    

   2.2 Three brands of empiricism    

The type of scientific anti-realism championed most effectively by van Fraassen is the one contemporary account of causality and causal modality that can unambiguously lay claim to the coveted title 'empiricism'. According to this robust empiricism, accepting a scientific theory involves embracing as true only what the theory has to say about the observable world. So even while disavowing the logical positivists' syntactic strategy for isolating the empirical content of scientific theories, van Fraassen nonetheless retains their abhorrence of metaphysics by insisting that it is no part of genuine science to believe in the literal truth of talk about causal processes, causal structures, causal powers, or other 'unobservables':    

To be an empiricist is to withhold belief in anything that goes beyond the actual, observable phenomena, and to recognize no objective modality in nature. To develop an empiricist account of science is to depict it as involving a search for truth only about the empirical world, about what is actual and observable. Since scientific activity is an enormously rich and complex cultural phenomenon, this account of science must be accompanied by auxiliary theories about scientific explanation, conceptual commitment, modal language, and much else. But it must involve throughout a resolute rejection of the demand for an explanation of the regularities in the observable course of nature, by means of truths concerning a reality beyond what is actual and observable, as a demand which plays no role in the scientific enterprise.[8]  

A second, more circumscribed form of empiricism embraces a realist understanding of causality and causal modality, but attempts to conserve as much Humean empiricism as is possible within that constraint. The best recent example is the position painstakingly laid out by Michael Tooley in Causation: A Realist Approach.[11] While insisting on the objective reality of causality and laws of nature, Tooley cites two rather persuasive considerations in support of his contention that he remains an 'empiricist' nonetheless.    

First, on his account the laws of nature, conceived of as modal relations of a special sort obtaining among universals, are metaphysically contingent; he does not argue for this thesis, but simply professes his allegiance to "the traditional empiricist view."[12]    

Second, as Tooley sees it, causal terms express theoretical rather than empirical concepts; that is, they are non-primitive terms that "do not refer to what is immediately given in experience" and are thus to be analyzed by means of non-causal terms.[13] What follows, by Tooley's own admission, is that Elizabeth Anscombe's random catalogue of simple causal verbs--viz., 'scrape', 'push', 'wet', 'carry', 'eat', 'burn', 'knock over', 'keep off', 'squash', 'make', and 'hurt'--contains no empirical terms, at least no purely empirical terms.[14] This is a very Humean claim indeed; in support of it Tooley produces a venerable empiricist (and occasionalist) argument that has close counterparts going back at least as far as the eleventh-century Islamic philosopher al-Ghazali, viz., that "there is no observable difference between a world in which all the non-causal facts are as they would be if states of affairs were causally related, and a world in which the states of affairs in question really are causally related."[15] However, as far as I know, Tooley stands alone in endorsing both this argument and also realism with respect to causality in nature. And while I am not convinced by the arguments he brings to bear, within this empiricist framework, against the anti-realist attempt to reduce singular causality to the mere subsumability of singular causal facts under generic 'lawlike' facts,[16] there is no doubt that he has staked out a distinctive intermediate position that deserves careful consideration.    

While Tooley's position is developed with an abundance of metaphysical sophistication and a marked sensitivity to the subtleties of fundamental ontology, the same is not generally true of those contemporary positions that tend toward an empiricism more Aristotelian than Humean in spirit. The reason is that the most important advocates of these positions have, at least lately, been philosophers of science who are more concerned with methodological and epistemic issues surrounding the discovery of causal connections than with abstruse metaphysical questions regarding the nature of causality and the ontology implicated by real causal relations. Oftentimes pertinent ontological issues are simply mentioned in passing and deferred for future consideration; occasionally they are disregarded altogether. (Here we can begin to see how a well-developed ontology like Suarez's might play a useful role in contemporary philosophy of nature.) However, many of the relevant authors--among whom I number, for example, Rom Harré and Edward Madden, Ernan McMullin, the later Wesley Salmon, Nancy Cartwright, and Paul Humphreys--have the distinct advantage of being able to relate questions about causality and causal modality directly to scientific aims and practices.[17] This imparts to their writings an important dimension often absent from the work of analytic metaphysicians.    

As I see it, there are three main assumptions, not always explicitly acknowledged, common to the positions that are 'empiricist' only in this weakest sense.[18] The first is that causality cannot be analyzed reductively by means of non-causal concepts; hence, one or more causal primitives will figure prominently in any general metaphysical account of efficient causality.[19] Of course, primitive notions can be more or less illuminating or fruitful, and so a choice among the plausible candidates will by no means be trivial.    

The second assumption is that singular causal facts are metaphysically prior to more general causal facts such as regularities or so-called laws of association. One corollary of this assumption is that causal relations, including deterministic ones, may obtain even in the absence of conditions that would engender causal regularities, at least easily identifiable regularities. Indeed, both Cartwright and Humphreys go so far as to assert that because of the multiplicity of interfering factors present in nature, there are in fact, outside the laboratory, very few regularities of the sort Humean empiricists have traditionally appealed to.[20] What's more, the regularities that do obtain are mere byproducts of the continuous integration of basic causal structures or tendencies with contingent background conditions of a sort that preclude widespread interference with the normal course of causal processes (where the term 'normal', as used in this context, has a normative and indeed teleological import).[21] As Cartwright puts it:    

We all know that the regularity of nature so central to the more conventional picture is a pretence ... Nature, as it usually occurs, is a changing mix of different causes, coming and going; a stable pattern of association can emerge only when the mix is pinned down over some period or in some place. Indeed, where is it that we really do see associations that have the kind of permanence that could entitle them to be called lawlike? The ancient examples are in the heavens, where the perturbing causes are rare or small in their influence; and the modern examples are in the physics laboratory, where our control is so precise that we ourselves can regulate the mix of causes at work. Otherwise, it seems to me, these vaunted laws of association are still very-long-outstanding promissory notes: laws of association are in fact quite uncommon in nature, and should not be seen as fundamental to how it operates.[22]  

The third common assumption is that the fundamental explanatory principles of natural phenomena are ontologically grounded in the things themselves. Beyond this, however, there is disagreement. Some, such as Salmon and Humphreys, evince an almost Humean aversion to irreducible causal powers or tendencies and contend that an ontological commitment to causal structures and processes is fully sufficient to yield at least limited causal laws that are relativized to carefully restricted reference groups or populations.[23] By contrast, Cartwright--and here she has Harré and Madden on her side--argues that deep and important suggestions by Salmon and others about how causes are to be "read off" from statistical correlations already presuppose an ontology that includes irreducible powers and tendencies in addition to causal structures and processes.[24]    

Since I side with Cartwright on this issue, I will not hesitate in what follows to talk freely of causal powers (tendencies, capacities, propensities) as entities distinct from the things that have them. However, nothing I say in this paper should be construed as an argument against the thesis that such talk is eliminable in favor of talk about structures and processes. I will simply leave that question aside.    

The three assumptions just noted provide much grist for the ontological mill: What is the nature of causality? Which causal primitives should we take as basic? Will such primitives allow us to distinguish adequately between the concept of an active or efficient cause and related "non-reducible concepts like those of enabling conditions, precipitating factors, triggers, inhibitors, preventatives, and the like"?[25] What sorts of entities are causal structures and causal actions or processes? What kind of background ontology can they be embedded in? What is the relation between causality and action? If tendencies and powers are indeed entities distinct from structures, how are they related to the things that have them? Are there interesting differences among types of efficient causes? How can we fruitfully characterize the difference between direct and indirect modes of efficient causality? How should we analyze natural necessity and objective probability?    

This is just a sample of the ontological questions that any neo-Aristotelian philosophy of nature will eventually have to face up to. And what the current emergence of Aristotelianism among philosophers of science suggests, I believe, is that (i), contrary to much anti-Aristotelian propaganda from the seventeenth century on, these ontological questions are not wholly removed from or foreign to properly scientific aims and practices, and that (ii), contrary to the impression sometimes given by twentieth-century Thomistic philosophers of nature, the actual aims and practices of modern empirical science, given its emphasis on measurement and mathematical techniques, are not inherently inimical to or incommensurable with a general Aristotelian metaphysics of nature. In short, we are at an especially propitious moment for coming to appreciate how an Aristotelian philosophy of nature might fruitfully draw upon, interact with, and complement the empirical sciences.    

In what follows I will address some, though not all, of the ontological questions raised above. Before doing so, however, I want to draw attention once again to the fact that today's neo-Aristotelians have not explored these questions very thoroughly; it is as if they see themselves treading along an unmarked path. But, of course, others have in fact walked before them. And even if we ultimately decide that the philosophy of nature propounded by the late medieval scholastics must be rejected or significantly altered, it will still be beneficial and enlightening to have before us at least one clear proposal for what a neo-Aristotelian metaphysics of nature might look like. It is with this in mind that I turn to Suarez.  
    

     2.3 Why Suarez?    

Granted that we would be well-advised to look to medieval Aristotelanism for a map of this 'novel' ontological terrain, the question arises: Why focus on Suarez? My reasons are three.    

First of all, Suarez is a brilliant, technically proficient, and profound metaphysician; to my mind, among the medieval Christian scholastics he ranks second only to Aquinas. Unfortunately, he has also been a neglected philosopher. As a near contemporary of Galileo and Descartes, he was largely eclipsed by the sixteenth-century humanistic revival and by the seventeenth-century revolution in science and philosophy--despite the fact that he was read and admired by Leibniz and at least read, if not admired, by the likes of Malebranche and Berkeley. More poignantly, he generally received short shrift even during the scholastic revival of the late nineteenth and early twentieth centuries, dominated as it was by what Ralph McInerny has called Thomists of the strict observance.[26] So both within and without the tradition of Aristotelian scholasticism, few have read his metaphysical works. To be sure, the Disputationes Metaphysicae are dense and difficult and chock full of arguments--just the sort of work that humanists and others with anti-metaphysical proclivities have always been fond of ridiculing. Nonetheless, for those of us who see a deep consonance between the perennial pursuit of wisdom and close metaphysical analysis, these disputations are a veritable treasure chest.    

Second, the Disputationes Metaphysicae contain, as far as I know, the deepest and most relentlessly sustained philosophical tract ever written on causality from an Aristotelian perspective; by my own calculation, a translation of Disputations 17-19 would take up approximately 600 manuscript pages. What's more, Suarez deliberately chose to write the Disputationes Metaphysicae as a "purely philosophical" propaedeutic to the study of revealed theology, and so it is not necessary, as it often is with his scholastic predecessors, to search widely through his theological works in order to isolate properly philosophical treatments of a given metaphysical topic; as a result, his discussion of efficient causality is more readily accessible to secular readers who have little interest in theology. I do not mean to imply, of course, that all the concepts Suarez makes use of will be immediately familiar to contemporary philosophers. But the same holds true for virtually all the important figures in the history of philosophy; what one needs is some philosophical motivation, of the sort I have tried to provide above, for expending the effort necessary to gain entry into Suarez's conceptual framework.    

Third, Suarez is not only an outstanding philosopher in his own right but also an gifted and erudite historian of philosophy who is thoroughly familiar with Hellenistic, Patristic, Jewish, and Islamic sources. In addition, because he comes upon the scene late in the sixteenth century, he is in a position to draw upon all of his most important scholastic predecessors. The result is a synthesis of impressive proportions; problematic issues are lucidly delineated, and the best arguments thus far for the main competing positions are laid out in depth. So through Suarez's work on efficient causality one has access to the best of pre-modern Aristotelianism as well as to the various anti-Aristotelian strains that he and his forebears had to contend with. 
    

3. Ontological Presuppositions 
 
     3.1 The big picture    

Like other medieval Aristotelians, Suarez takes efficient causality to be a relation holding between entities that act (agents) and entities that are the recipients of actions (patients). In a typical case (excluding creation ex nihilo, which I will return to below) one or more agents act upon a patient in such a way as to produce or conserve an effect, where the effect is itself either a substance or an accident, i.e., an intrinsic determination or modification of a substance. More technically, an agent's action on a patient is simultaneously (i) the exercise of an active causal power on the part of the agent and (ii) the actualization within the patient of a formal determination for which the patient, given its intrinsic constitution, has an antecedent potentiality. Accordingly, we can distinguish active from passive causal powers. A substance's active causal powers delimit the range of effects it is capable of directly producing or conserving when it acts upon suitably disposed patients in appropriate circumstances, whereas its passive causal powers delimit the range of effects that might be produced or conserved when it is acted upon by suitably situated agents in appropriate circumstances.    

This general portrait has two noteworthy ontological corollaries. The first is that, contrary to one influential opinion in contemporary metaphysics, it is substances and their accidents, rather than events, that serve as the relata of the causal relation. Though it does not follow forthwith that from an Aristotelian perspective talk of so-called 'event causation' is utterly wrongheaded, it does follow that every instance of event causation involves, at the deepest metaphysical level, the action of agents on patients.[27] Indeed, the medieval Aristotelians, sensibly to my mind, conceive of the whole natural world, inanimate as well as animate, as a dynamic system of interrelated and interacting entities endowed by nature with causal tendencies and susceptibilities and always poised to produce their proper effects in the appropriate circumstances. It follows that 'agent causation' is a pervasive feature of the physical universe and is not limited just to substances endowed with sentience or intelligence or the power of free choice.    

The second corollary is that some version of a substance/accident ontology is fundamentally correct. A substance is conceived of as a 'this-such', i.e., a basic unified entity with an essential nature that constitutes it as a member of some natural kind. (Artifacts that incorporate such basic entities into a unified system may be considered substances in an extended sense.) Since from an Aristotelian point of view the paradigmatic examples of substances are complex living organisms, the version of substance/accident ontology employed by Suarez is also anti-reductionistic. That is to say, a formal or structural principle (a substantival or substantial form) may subsume substances of a lower order (the proximate matter) into a higher-order unity with distinctive properties that are irreducible to the properties of the individual constituents or of a mere coincidental aggregation thereof. In such a case the lower-order entities lose their independent status as substances and become, at least for the time being, mere parts of a substance.    

A substance functions as the subject of its accidents, where an accident is conceived of as an intrinsic formal perfection or determination or modification of a substance which is ontologically distinct from the substance and is an individual entity in its own right with its own 'accidental' (as opposed to 'substantival') being. In general, an accidental entity (in technical terminology, an 'accidental form') is apt by its nature to 'inhere in' or 'belong to' a substance that has substantival being of a sort consonant with its serving as the subject of such an accident. Some of a substance's accidents, including its basic active and passive causal powers, are 'inseparable' accidents that flow directly from the substance's nature or essence as definitive of its kind, while others are 'separable' accidents that are consonant with its nature but not endemic to it.[28]    

In this connection I should also note that even within the confines of a substance/accident ontology disagreements have arisen historically over the exact ontological status of accidents. Suarez himself, for instance, distinguishes among more and less independent types of accidental entities. Whereas he (i) treats sensible qualities, habits, causal powers, and three-dimensional quantity as 'full-fledged' accidents that are 'really distinct' from substances and can thus, at least by God's power, exist on their own independently, he (ii) regards motion, position, acting, and being acted upon as mere 'modes', incapable in principle of existing independently and thus only 'modally distinct' from the things that have them, and (iii) holds that relations do not constitute a separate and irreducible category of real beings at all. Yet each of these three claims is contested in whole or in part by other scholastics.[29] I raise this issue only to intimate the range of possible substance/accident ontologies, and I will not pursue it any further here except to mention that an indispensable element of Suarez's own account of efficient causality is the claim that every proper effect of an efficient cause is an entity that has real being of some sort or other; that is, every proper effect must be either a substance or a full-fledged accident or at least a mode.    

So much for the basic picture. 
    

      3.2 On behalf of substance and accident    

Of course, it is hardly necessary to point out that substance/accident ontologies are viewed with deep suspicion by many contemporary philosophers, including some of the very people whom I would label neo-Aristotelians. So even though this is not the place to explore the relevant issues in any great depth, I do want to indicate briefly why, to my mind, certain standard objections to substance/accident ontologies are less than conclusive, especially within the context of recent developments in analytic metaphysics and epistemology.    

Let's look first at the Aristotelian conception of substance. An initial reservation has to do with the role of a substance as the subject or substratum of accidents that are ontologically distinct from it. Dorothy Emmet, after having argued in a typically Aristotelian vein that it is 'continuants' rather than 'occurrents' that are efficient causes in the most basic sense, nonetheless refuses to identify continuants with substances:    

[The distinction between 'continuants' and 'occurrents'] answers to the traditional distinction between substances and events. The 'continuant', however, need not carry the metaphysical implications which sometimes were seen in 'substance', as being a substratum distinct from its qualities. A continuant need only show a persistent character recognisable over time. 'Occurrents' are changes in a continuant, for example this particle as moving from A to B at time t ... When one continuant is seen as external to another and acting on it, this is transeunt causation. When there is a change of state within a single continuant, this is immanent causation. Changes within a system taken as a whole are cases of immanent causation. But a system may be seen as composed of parts which are subcontinuants, and where changes in the system can be explained as due to the action of these on each other, they can be seen as cases of transeunt causation.[30]  

Of course, if an Aristotelian substance were a Lockean 'I know not what' or, in modern parlance, a 'bare particular' that underlies its accidents without having any characteristics or formal determinations in and of itself, then it would indeed be ontologically suspicious. But neither Suarez nor any other faithful Aristotelian thinks of a substance in this way. As emphasized above, an Aristotelian substance is a 'this-such'--an oak tree or an aardvark or a hydrogen atom, for example--and not a bare 'this'. The 'such' of 'this-such' points precisely to the inseparability of a substance from the formal determination (in technical terminology, the 'substantial form') that constitutes it as a member of a given natural kind. Thus, when a substance is said to 'underlie' or to 'be the subject of' its accidents, this way of talking represents little more than a generalization over ordinary accidental attributions such as 'This oak tree is eighty feet tall' or 'Aardvarks have a tendency to seek out and devour insects.'    

Admittedly, the claim that an observable material substance underlies its sensible accidents carries with it the implication that such a substance possesses a metaphysical depth, so to speak, that is not immediately evident from ordinary sense perception; but it is difficult to see why anyone antecedently sympathetic to scientific realism should be bothered by this. Moreover, just as on Emmet's view continuants have parts (subcontinuants) that act on one another, so too on the standard Aristotelian picture complex natural substances have what we might call 'powerful parts' that produce and conserve effects in one another. However, one implication of Aristotelian anti-reductionism is that such action must be attributed ultimately to the substance as a unified whole whose principle of organization (substantial form) directs and modifies the operations of its parts; otherwise, complex substances such as living organisms (or, for that matter, chemical elements or physical atoms) would be mere coincidental aggregations of substances rather than individual substances in their own right.    

A second reservation about the Aristotelian conception of substance centers around its unabashed commitment to essentialism. In expressing her disapproval of the theory of causal powers set forth by Harré and Madden, Emmet has this to say:    

[I should not] want to talk about continuants as having 'intrinsic natures, shown in causal powers'. This seems to me to savour of a hankering after Aristotelian real definitions, which are then made effective as formal causes; it does not allow enough for radical changes in continuants. Rather than talking about 'natures' I should prefer to think of a thing having, in Locke's phrase, a 'real internal constitution', maintained dynamically, partly through internal homeostatic 'feedbacks', in which an aberration at one stage may be corrected at the next ... This carrying forward of a pattern, perhaps in a rhythmic reiterative form, may go both for fundamental particles, the distribution of whose activities is given in the mathematics of wave mechanics, and also for organisms, and for whatever other natural units there may be in between.[31]  

Beyond this, it is worth noting that one of the most striking features of recent analytic philosophy has been the resurrection of metaphysical essentialism.[32] Talk of natures and essential properties abounds in places where only twenty years ago it would have been deemed archaic and out of step with the modern mind. Of course, this development is not, taken just by itself, an argument in favor of essentialism; however, it is clear at least that the friends of substance/accident ontologies are not nowadays in the position of having to shoulder by themselves the burden of defending essentialism.    

A third reservation about the Aristotelian conception of substance is epistemological in nature: If substances 'underlie' their sensible accidents, are they not in principle unobservable? An Aristotelian might be tempted to reply glibly that substances are in principle unobservable only if oak trees and aardvarks are. Yet flippant though it be, this response reflects an attitude that has become almost commonplace in current analytic epistemology. Rejecting the concession phenomenalists had made to skepticism regarding external objects, most contemporary epistemologists hold that it is perfectly proper for us to repose without further argument in our basic pre-analytic conviction that we have sensory cognition of substances themselves as well as of their sensible characteristics. To be sure, epistemological realists of this sort must draw a distinction between the way in which substances are available to the senses and the way in which sensible characteristics like colors, shapes, sounds, and smells are. According to Aquinas, for example, sensible accidents are the per se objects of sensation, whereas substances (along with easily identifiable efficient causes) are per accidens or incidental objects of sensation; the idea is that material substances (and causes) are sensed 'in and through' the sensing of their accidents (and effects).[33] Still, the observability of substances is not thereby called into question.    

A related consideration is that according to Aristotelians our initial conceptual grasp of a sensible substance--by means of what Suarez and other medievals call a 'quidditative' concept and what contemporary philosophers call a 'natural kind' concept--provides us only with a starting point for inquiry into the nature of that substance, regardless of whether that inquiry is of the unsystematic sort typical of ordinary life with its overriding practical concerns or of the systematic sort peculiar to the natural sciences. In both cases it is only through further experience and experiment (both expressed by the Latin term experimentum) that we can learn about the characteristic effects of such substances and on that basis come to a knowledge of their powers and of the natures associated with those powers.    

This point is intimately connected with the doctrine of 'real definition' impugned by Emmet in the last passage quoted above. The traditional empiricist resistance to an Aristotelian account of real (as opposed to merely nominal) definition seems to have been founded at least in part on the fear that such definitions are meant to serve as the basis of an a priori science that simply deduces the properties of substances from their definitions alone, without any further appeal to experience. However, within an Aristotelian logic of discovery the role of real definition is in fact limited to establishing a preliminary taxonomy of substances which might order and guide further inquiry; and, even then, any taxonomy thus arrived at is able to be expanded and (at least partially) revised in light of future experience and experiment.    

Let me now turn briefly to accidents. As I mentioned above, Suarez's account of efficient causality presupposes that accidents--whether full-fledged accidents or mere modes--are individual beings that inhere or are present in the substances that are determined or perfected by them. Accordingly, his substance/accident ontology differs from the more Platonistic substance/property ontologies popular among contemporary essentialists, where properties or attributes are thought of as abstract entities that are 'exemplified' by concrete substances. Interestingly, Suarez is willing to countenance properties of this sort as long as they are identified with ideas in the mind of God and as long as exemplification (or participation) is thought of as a relation that substances bear to those ideas by virtue of God's creative activity. However, he also insists that accidents are concrete individual entities in their own right. The issues here are difficult and complex, and I do not want to rule out antecedently the suggestion that an Aristotelian account of efficient causality can be reformulated without loss within the confines of a Platonist ontology of substance and property. Still, my own conviction is that such an ontology is too abstract and in some ways too coarse-grained to serve in this capacity, though I will not argue the point here.  
    

4. Suarez on Efficient Causality    

     4.1 A gloss on Aristotle's definition    

Suarez begins Disputation 17 with an extended reflection on and reconstruction of Aristotle's definition of an efficient cause as "that whence there is a first beginning of change or rest." Though Suarez expresses his own revised definition in a number of alternative ways, I believe that the following formula captures all the essentials:  

x is an efficient cause of y if and only if x is an extrinsic principle from which y emanates by the mediation of action. 

The material and formal causes of an entity y are called intrinsic principles of y because they are constitutive of y and determine the sort of substance or accident it is. Suarez puts it as follows:    

The formal and material causes ... cause their effect by giving to it their own proper being [entitas], and this is why they are called intrinsic causes.[34]  

The efficient cause is an extrinsic cause, i.e., a cause that does not communicate its own proper and (as I will put it) individual being [esse] to the effect, but rather communicates to it a different esse which really flows forth and emanates from such a cause by the mediation of an action.[35]  

The notion of action also grounds the metaphysical distinction between genuine causes on the one hand and mere background conditions, or what Suarez calls sine qua non conditions for acting, on the other. Under this latter heading he includes, for example, the required proximity of the agent to the patient, the removal of impediments, and the presence of mere catalysts for action. Still, because such conditions "fall under scientific knowledge" and are "some sense per se with respect to physical necessity,"[37] they must be treated at length in any comprehensive account of efficient causality--a task that Suarez himself carries out in sections VII-IX of Disputation 18. However, from the very beginning he cautions:    

Because a sine qua non condition of this sort agrees with a per se principle of action in being necessarily required, in some cases it is not easy to discern in which of the two ways a given disposition or property of a thing concurs with respect to an action, i.e., whether it concurs as a per se principle or only as a sine qua non condition.[38]  

The final salient element in Suarez's definition is the emanation of y from x. Suarez intends this notion to cover y's being produced by x after not having existed as well as its being conserved in existence by x after its production. So both production and conservation fall under the general rubric of efficient causality. However, as the last quoted passage makes clear, such emanation is not to be construed as the communication to y of x's own being or of some part of x. In particular, it is not the case that x communicates its own individual formal determinations to y--as if numerically the same substantial or accidental form might "jump" or be transferred from one subject (the agent) to another (the patient). As Suarez is well aware, certain occasionalists seem to have thought, to the contrary, that an Aristotelian account of efficient causality does indeed entail just such a transfer of forms, and they had argued from the absurdity of this idea to the conclusion that there is no action or efficient causality in the physical universe. In reply Aquinas had clarified the matter as follows:    

It is ridiculous to argue that bodies do not act by appealing to the fact that no accident passes from one subject into another. For a hot body is said to produce warmth not in the sense that numerically the same heat that is in the heating body passes into the heated body, but rather because by virtue of the heat which is in the heating body a numerically distinct heat comes to exist actually in the heated body--a heat that previously existed in it in potentiality. For a natural agent is not something that transfers its own form into another subject, but is instead something that brings [reducens] the subject which is acted upon from potentiality to actuality.[40]  

My second reason for broaching this issue is that Hector-Neri Casteñeda has, in light of the skeptical worry, recently argued that what is distinctive about real efficient causality is precisely the transfer of what he calls 'causity' from the cause to the effect:    

Whatever the profound metaphysics of time and causality may be, the crucial thing is that on the surface of it causation is communication and transmission of something in the cause to the effect, whether by replication or by actual carrying over across time. This transfer of something, including the transfer of certain orderliness, is the substance of causation.[42]  

Casteñeda goes on to develop a number of strictures on the notion of causity, and identifies energy as conceived by contemporary physics as at least one form that causity can take.    

It is unclear to me at this point whether Aristotelians must immediately reject Casteñeda's position, since I am not confident that I understand it fully. However, St. Thomas's comments put at least one ontological constraint on an acceptable notion of causal communication or transmission, viz., that it not involve the transmission of numerically the same form or determination from agent to patient. What's more, even if the transfer of something like what Casteñeda has in mind is indeed an essential ingredient in efficient causality, the skeptical argument and Aquinas's reply to occasionalism nonetheless call our attention to the fact that, familiar though it be, efficient causality is at its core a puzzling and even somewhat mysterious feature of reality.[43] Yet--or so at least an Aristotelian would maintain--it is better to have one's deep philosophical mysteries emerge near the end of inquiry rather than, as with the occasionalist and Humean denial of causal action in nature, at the very beginning.    

Be that as it may, we have now examined the main elements of Suarez's basic account of efficient causality. There is just one other Suarezian distinction I want to introduce, viz., the distinction between an efficient principle ut quod and an efficient principle ut quo, i.e., the distinction between (i) the entity which exercises a power and to which the resulting action is ultimately attributed and (ii) the power or faculty by which such an entity operates. I mention this in passing simply because several of the questions concerning efficient causality that Suarez deals with in Disputations 17-19 center around the principle ut quo, and it is important to understand from the beginning that Suarez takes such principles to fall under his general definition. (One who denies that there is a real distinction between a substance and its powers will in any case have to reconstruct this distinction in some way, perhaps by treating powers as mere modes or states of substances.)    

I will now try to explicate in a bit more detail and to formulate a bit more precisely the rudiments of Suarez's general account of efficient causality. Within the limits of the present paper my main goal will be to capture the basic distinction between what Suarez calls immediate and per se efficient causes, which alone are causes "in the proper and absolute sense,"[44] and efficient causes whose influence on a the effect is more indirect. The latter fall under the broad category of what Suarez calls per accidens causes, but he himself maintains that per accidens causality is itself too diverse and variegated a notion to be captured by a single unified account, since at least certain elements in traditional Aristotelian discussions of per accidens efficient causality "pertain more to modes of predicating than to modes of causing."[45] So I will be concerned only with those types of per accidens causes that I take to be philosophically and scientifically interesting. Following Suarez, I will call them mediate causes. Mediate causes do, I believe, lend themselves to a unified account, even though, as I will suggest below, a full treatment of efficient causality would have to include a more fine-grained analysis of the various distinct ways in which agents can make indirect causal contributions to a given effect. 
    

      4.2 Per se efficient causality    

As indicated above, at the heart of Suarez's account of ordinary efficient causality lies the notion of the communication of formal determinations or perfections to a patient by an agent through the mediation of action. However, because Suarez sees creation ex nihilo as an instance of efficient causality, he speaks more generally of the communication of being or esse by means of action. This allows him to accommodate the theological belief that at least one sort of action does not presuppose a preexistent recipient or patient. In such a case the recipient and all its constituents, material as well as formal, come into existence as the result of the action; to put it succinctly, creation ex nihilo involves the communication of esse 'from the bottom up'.    

Suarez thus has a deepseated theological motive for moving from Aristotle's idea of the communication of form to the more general Thomistic idea of the communication of esse. However, there are also perfectly respectable philosophical reasons for constructing a general account of efficient causality in such a way as to provide conceptual space for the thesis that creation ex nihilo is metaphysically possible. First of all, it seems obvious that if there is such an action as creation, it is indeed an instance of efficient causality. What's more, since the possibility of creation is a substantive philosophical issue that historically has spawned an extremely interesting and fruitful debate, the question of whether creation is possible should not, it seems, be decided antecedently one way or the other by what purports to be a general account of efficient causality. Instead, the correct order of proceeding, at least initially, is to formulate an account of efficient causality and then address questions concerning creation. This is, in fact, Suarez's own strategy; immediately after treating efficient causality in Disputations 17-19, he turns, in Disputation 20, to an extended discussion of creation, including the question of whether creation is metaphysically possible.[46] Of course, if there turn out to be compelling arguments against the possibility of creation ex nihilo, then this may lead us in the end to reformulate our general account of efficient causality in such a way that it entails that every action involves a preexistent patient. But such an account should emanate from an extended debate and not from an a priori stipulation.    

With this in mind, I will adopt as my first causal primitive the locution 'x, by acting, directly communicates esse to y at t', where (i) x and y are either substances or accidents, (ii) t is a time, (iii) the phrase 'by acting' is meant, in accordance with what was said above, to distinguish an efficient cause from the other three types of Aristotelian causes, and (iv) the phrase 'directly communicates esse' is meant to distinguish efficient causality in the most proper sense from the more indirect modes of efficient causality that I will be discussing below under the category of mediate efficient causality. Also, as I am using this locution, it implies that y exists at t and that t is the time of x's action. (I put this last point somewhat indirectly because even those who, like St. Thomas, insist that God is not intrinsically measured by time nonetheless allow that God acts 'in time' in the sense that his transeunt or external actions are to be identified with the effects that he produces in time.)    

This first primitive locution gives us all the resources we need to characterize the Suarezian notion of per se and immediate efficient causality. But before I get to that, I want to say a bit more about the Thomistic notion of esse which Suarez makes use of here. In order to elucidate the broader context in which this notion is most at home, I will touch upon the theological theme of the relation of finite creatures to their transcendent creator; however, the theological overtones are not part of the account of per se efficient causality as such.    

According to St. Thomas, esse is a principle of actuality, where the notion of actuality is broadly construed to encompass any positive determination or perfection, including active and passive causal powers and the entities that come to exist through the exercise of such powers. So communicating esse entails giving perfection of some sort or other, i.e., giving existence to a substance by actualizing a particular concrete nature with the set of "specifying powers" endemic to its natural kind, or giving existence to an intrinsic accidental determination of a substance.    

Finite entities are said to 'participate in' or 'have a part of' esse as such. This is because all such entities have some proper part of, or finite share in, the whole gamut of possible perfections; in other words, they have esse as limited by their natures to what we might in general call such-esse and to what in each particular case is the sort of actuality proper to the entity's nature and accidental determinations. So, for instance, a white oak tree has white-oak-tree-esse and, subordinated to it, the sorts of esse proper to its various separable and inseparable accidents. Again, a human being has human-esse, a photon has photon-esse, and so on. This explains the spirit behind St. Thomas's claim that for a living organism to exist is for it to be alive, i.e., to have a sort of esse or actuality appropriate to living organisms. Thus the term 'esse', unlike the term 'exists' in at least one common use, admits of degrees or at least of distinct grades, even though 'to have esse' and 'to exist' are equivalent in the sense that an entity exists if and only if it has some sort of esse.    

Given this general metaphysical picture, one might naturally think of created entities as being partially ordered from the less perfect to the more perfect according to the type of actuality (including causal power) they have. Such an ordering reflects the degrees or grades of esse, i.e., lesser and greater shares in the plentitude of perfections. What's more, as 'beings by participation' or 'participated beings', finite entities are such that they need not exist at all and hence must receive esse from causes distinct from themselves; in St. Thomas's terminology, there is in them a real distinction between esse and essence (or nature). It does not follow that in a given creature esse and essence are separable; it follows only that it is metaphysically possible that there should have been no such participation in esse.[47] According to St. Thomas, only God is such that in him there is no distinction between esse and essence; he is subsistent esse itself (ipsum esse subsistens), and so he cannot fail to exist and cannot fail to be 'unparticipated'--or, as it were, 'unpartitioned'--esse, a fully actual being who cannot be acted upon and who possesses all possible perfections in unlimited degree.[48]    

So it is the active communication of esse to an entity that constitutes the core of efficient causality, and Suarez's account presupposes that the production or conservation of any effect in nature involves some agent's communicating esse of some sort to some recipient. This is true even when a patient suffers a loss or privation of esse as the result of an agent's causal influence--as, for instance, when a living organism dies or when someone is blinded by being struck in the eye. What occurs in such cases is the introduction into the patient of a formal determination which is incompatible with the form that the patient is thus deprived of. Such examples should make us aware that even though every instance of efficient causality involves a giving of esse or perfection, this does not mean that the patient is itself more perfect absolutely speaking as a result of the agent's influence.    

Given this background, we are now in a position to appreciate Suarez's characterization of a per se and immediate efficient cause:    

A per se cause is a cause on which the effect directly depends with respect to that proper esse which it has insofar as it is an effect. And since this cause alone is a cause in the proper and absolute sense, almost the whole next disputation [Disputation 18] will be concerned with it alone.[49]  

More formally,  

x is a per se and immediate efficient cause of y at t if and only if x, by acting, directly communicates esse to y at t. 

Suarez goes on to distinguish two main types of per se causes, viz., principal and instrumental, where an instrumental cause is, in general, an agent that is employed in some way by a principal cause in effecting its own proper effect. Suarez spends the greater part of section II of Disputation 17 canvassing four competing accounts of this distinction before finally devising his own. Without going into detail, I will note only that Suarez's own account presupposes an ordering, according to perfection or 'nobility', of causal powers and possible causal effects; in each case a given power is of itself either (i) proportioned to a given effect, i.e., "more noble than or at least as noble as the effect,"[50] or (ii) not proportioned to that effect, i.e., less perfect than the effect. The basic idea is that whereas a principal cause of a given effect is a fitting cause of the effect, an instrumental cause of a given effect must, in view of the sort of causal power it has just taken by itself, must act 'in the power' of a principal cause in order to be able to contribute to that effect. If we thus adopt as a primitive the locution 'x acts at t by a power that is proportioned to y', we can capture Suarez's distinction as follows:[51]  

x is a principal per se cause of y at t if and only if  
(a) x is a per se and immediate cause of y at t, and  
(b) x acts at t by a power that is proportioned to y. 

 x is an instrumental per se cause of y at t if and only if  
(a) x is a per se and immediate cause of y at t, and  
(b) it is not the case that x acts at t by a power that is proportioned to y. 

Needless to say, the notion of an hierarchical ordering of powers and effects stands in need of much more clarification, even though there are many intuitively plausible examples of instrumental causes, e.g., the tools of a craft, writing instruments, baseball bats, personal computers, and other entities that obviously require the action of a 'higher-order' principal cause in order to attain to effects like works of art, philosophical treatises, homeruns, etc. Suarez also produces more interesting and perhaps problematic examples, but I will leave this matter for future consideration.    

One last note. Not only does the distinction between principal and instrumental causes allows us to identify different levels of per se efficient causes, the present account also allows for cooperative per se action within those levels, so that a given effect might have a number of simultaneously acting principal causes or simultaneously acting instrumental causes. We can thus distinguish partial from total causes and distinguish both from background conditions. This is another topic that would have to be discussed at length in a full-blown theory of efficient causality.  
    

    4.3 Mediate efficient causality    

Per se causality involves the direct and immediate emanation of an effect from its cause or causes. It is obvious, however, that the term '(efficient) cause' is used to cover a broader range of causal contributions that can justifiably be thought to fall under Suarez's general definition of an efficient cause.    

For instance, x may be reasonably called an efficient cause of y if it bears to y just the anscestral of the relation of being a per se and immediate efficient cause. This may occur either diachronically or synchronically: x may have acted long ago to initiate or maintain an unbroken chain of causes, each of which is a per se and immediate cause of the next and the last of which is a per se and immediate cause of y; or x may be a per se conserving cause of z (or of a per se conserver of z, and so on) during the very time at which z is a per se and immediate cause of y. In both cases x is an efficient cause of y, but not a per se and immediate cause of y.    

Again, x might act as what Aristotelians call a 'disposing' or 'enabling' cause of  y. This, too, can happen in a number of ways: x may be a cause of y by virtue of its having acted to remove an impediment to z's being a per se cause of y, or more remotely, by virtue of its being a per se cause of an agent that removes an impediment to z's being a per se cause of y, and so on; or x may be an efficient cause of y by virtue of its having acted in such a way as to effect an enabling condition for z's being a per se cause of y--perhaps x moves z spatially closer to y, or perhaps x acts on the subject of y in such a way that that subject becomes susceptible to z's action, with the result that z is a per se and immediate cause of y.    

Where free agents are involved, x may be what Aristotelians call an 'advising' cause of y: it might happen, say, that x commands or asks or persuades or urges or counsels a free agent z to act in a given way, and that in part because of this z acts as a per se and immediate cause of y.    

The list of possibilities could presumably go on, and in a very complicated causal chain we might find that all of these modes of causal contribution, along with various combinations thereof, are involved in the production of a given effect.    

A complete theory of efficient causality would have to say more about each of the modes of causal contribution that are lumped under the category of mediate per accidens causality. However, my present concern is merely to formulate a simple and general characterization of indirect causal contributions of the sort in question. As I read Suarez, the key to such an account is the twofold claim that (i) an agent x is a mediate cause of a given effect y only if it is a per se and immediate cause of some effect z distinct from y (thus preserving the thesis that action lies at the core of efficient causality),[52] and that (ii) it is by virtue of its being a per se cause of z that x makes a causal contribution to y.    

So we have to introduce a causal primitive such as the following: 'by virtue of being a per se cause of z at t*, x causally contributes to y's existing at t', where x, y, and z are distinct substances or accidents, and t and t* are times. (I will not put any temporal ordering constraints on these times, lest I beg substantive philosophical questions regarding the possibility of backwards mediate causality; this issue should, like that of the possibility of creation ex nihilo, be argued on its own merits and not decided by stipulation.) The primitive locution in question implies that y in fact exists at t, but does not imply that x exists at t and says nothing about the specific nature of x's causal contribution. So, for instance, x might make its causal contribution to y's existing long before t and not even exist at any time proximate to t. Similarly, x's causal contribution to y's existing may be more or less closely connected with x's proper causal tendencies or (in the case of rational beings) intentions, and more or less determinative of the specific character of the effect.    

So we have:  

x is a mediate efficient cause of y at t if and only if  
(a) for some z (y) and t*, x is a per se and immediate cause of z at t*, and  
(b) by virtue of being a per se and immediate cause of z at t*, x causally contributes to y's existing at t. 

This completes the promised preliminary sketch of a Suarezian model of efficient causality. Clearly, much work remains to be done in order to turn what has been proposed here into a complete account of efficient causality. Still, I believe that even this sketch shows that what Suarez has to say about efficient causality fits very well into the general framework of neo-Aristotelian philosophies of science and that, at the very least, it is worthy of close study by contemporary metaphysicians and philosophers of science. 
    

5. Conclusion    

If much more work needs to be done, it is only fitting to take Suarez as one of our guides. In this concluding section I want to indicate briefly some of the questions that Suarez himself addresses in Disputations 18 and 19. Since it is impossible in so short a space to convey the richness and diversity of his discussions, I will highlight just those topics which are of most obvious relevance to current work on causality.    

In sections I-VI of Disputation 18 Suarez is working against the backdrop of anti-Aristotelian positions that either deny altogether that there is causal action in nature or else put undue restrictions on the range of effects that can be caused by natural substances. In section I he argues that occasionalism (and, by implication, Humean empiricism) is a philosophically unacceptable philosophy of nature by criticizing its foundations and drawing out various of its counterintuitive consequences. (This discussion is of some historical importance because Malebranche replies to it almost point for point in the Elucidations of the Search After Truth.) Other medieval philosophers, stopping short of occasionalism, had maintained that finite causes are capable of producing only accidents and not substances. So in sections II-VI Suarez delves into various issues surrounding the causal power and action of substances and accidents. Even though some of his examples, drawn from fairly pedestrian Aristotelian science, are outmoded, the philosophical issues at stake are almost always ones that have been or should be raised by contemporary neo-Aristotelians. For instance, section III contains a tract on the relation between substances and their active causal powers that is redolent of the current dispute, alluded to above, about whether causal powers are reducible to structures (forms) and processes (actions).    

In sections VII-X of Disputation 18 Suarez deals with various background condtions required for causal action. Among the issues he discusses are the requisite relations between an agent and the patient it acts upon; linear causal propagation and action at a distance; the distinction between immanent causality, in which an agent effects something within itself, and transeunt causality, in which an agent effects something outside itself; action and reaction; and the ontological relation between action and efficient causality.    

Disputation 19 is divided into two main parts. In sections I-IX Suarez discusses natural necessity and contingency along with the nature of free choice, including subtle questions about the relation between the cognitive and appetitive powers of rational beings. Then, in sections X-XII, he discusses chance, fortune, and contingency among effects in nature.    

What I have tried to do in this paper is to convey something of the nature, scope, and depth of Suarez's account of efficient causality and to make clear that, whatever judgment one might ultimately pass on Suarez's substantive positions, the ontological questions he raises in Disputations 17-19 cannot be long ignored by any philosophy of nature that rejects Humean empiricism in favor of a more Aristotelian alternative. 

1. Francisco Suarez, Disputationes Metaphysicae (hereafter: DM), vols. 25 and 26 of Suarez, Opera Omnia: Nova Editio, edited by Carolo Berton (Paris, 1866; reprinted in two volumes at Hildesheim, 1965).    

2.  In ethics I have in mind, for example, Alisdair MacIntyre's After Virtue (Notre Dame, IN: University of Notre Dame Press, 1981), along with the copious recent work on the virtues inspired at least in part by MacIntyre. The best example in the area of analytic epistemology is Alvin Plantinga's forthcoming three-volume work on epistemic warrant, in which a central role is played by the teleological notion of proper cognitive functioning. I will be referring below to corresponding works in metaphysics, but here will cite Elizabeth Anscombe and Peter Geach as well-known proponents of broadly Aristotelian positions on a wide range of metaphysical (as well as ethical) issues.    

Also, I mean neither to overlook nor to disparage the work by Thomistic philosophers in this century. Indeed, on topics related to causality I have learned much from perusing Thomistic writings in metaphysics and the philosophy of nature. Among them are Vincent Smith, Philosophical Physics (New York: Harper and Brothers, 1950) and The General Science of Nature (Milwaukee: Bruce Publishing Co., 1958); Charles Hart, Thomistic Metaphysics (Englewood Cliffs, NJ: Prentice-Hall, 1959); and Richard Connell, Substance and Modern Science (Houston, TX: Center for Thomistic Studies, 1988). However, it is fair to say that such work has fallen well outside the mainstream of Anglo-American philosophy, a fact that is traceable partly to the self-imposed isolation of Thomists themselves and partly to the general hostility toward classical metaphysics that characterized mainstream analytic philosophy in the early and middle decades of this century.    

3. In saying this I am glossing over deep and interesting questions about the notion of a natural kind, the distinction between natural and artificial kinds, and the bearing of scientific realism on taxonomic issues. For an extensive treatment of these questions from a realist perspective, see Frederick Suppe, The Semantic Conception of Theories and Scientific Realism (Urbana, IL: University of Illinois Press, 1989), pp. 201-265.    

4. In "The Necessity of Nature," Midwest Studies in Philosophy 11 (1986): 215-242, I attempted to give an account of natural necessity along these lines.    

5. Laws and Symmetry (Oxford: Clarendon Press, 1989), p. viii.    

6. The Scientific Image (Oxford: Clarendon Press, 1980), p. 155.    

7. Laws and Symmetry, p. 185. Interestingly, van Fraassen's accusation that realists conceive of scientific explanation as irreducibly special has--or so it seems to me--its greatest rhetorical force when directed at those who, like Michael Tooley, take the fundamental explanatory principles or laws of nature to be 'laws of strict necessitation' that entail exceptionless regularities in nature and are themselves distinct from ascriptions of basic causal tendencies. See Tooley's Causation: A Realist Approach (Oxford: Clarendon Press, 1987), pp. 39-40. For it is relatively clear that laws of nature in this sense play little if any role in non-scientific explanatory contexts.    

From an Aristotelian perspective, on the other hand, laws of nature so conceived either (i) are completely otiose, as Nancy Cartwright contends in Nature's Capacities and Their Measurement (Oxford: Clarendon Press, 1989), esp. p. 185, or else (ii) must be thought of as divine commands regarding nature, commands that are to be integrated into an Aristotelian philosophy of nature in much the same way that Aquinas integrated divine ethical commands into Aristotle's naturalistic moral theory. Thus, from a Thomistic-Aristotelian point of view, the notion of a law of nature divorced from the idea of God as lawgiver is an anomaly within the philosophy of nature in just the same way that, according to Elizabeth Anscombe, the notions of moral law and moral obligation, once divorced from the idea of God as moral lawgiver, are anamolous within modern moral theory. See Anscombe's "Modern Moral Philosophy," Philosophy 33 (1958): 1-19.    

There is an interesting historical corollary to this point, viz., that the emergence of the notion of a law of nature to a position of centrality within seventeenth century science and philosophy was not just accidentally connected with the widespread rejection of Aristotelian philosophy of nature with its intrinsic grounding of causal principles. Van Fraassen expresses a similar sentiment in Laws and Symmetry, pp. 1-5.    

8. The Scientific Image, pp. 202-203    

9. The Scientific Image, p. 152.    

10. Laws and Symmetry, p. 214.    

11. I should also mention in this regard D.M. Armstrong's What is a Law of Nature? (Cambridge: Cambridge University Press, 1983), though Armstrong's allegiance to Humeanism is less pronounced than Tooley's.    

12. Causation: A Realist Approach, p. 320.    

13. Causation: A Realist Approach, p. 317.    

14. See Anscombe's "Causality and Determination," in Ernest Sosa, ed., Causation and Conditionals (Oxford: Oxford University Press, 1975), pp. 63-81.    

15. Causation: A Realist Approach, p. 28. Tooley's italics.    

16. These arguments are found in Tooley's discussion of the 'supervenience view'; see Causation: A Realist Approach, pp. 190-202. According to this view, which is a form of anti-realism with respect to causality, singular causal facts are supervenient upon non-causal facts. Tooley's own position is that even though causal terms must be analyzable by means of non-causal terms, it is not the case that causal facts are supervenient upon non-causal facts, i.e. that causal facts are "logically determined by the causal laws, together with the totality of non-causal facts" (p. 189). This combination of views, he argues, opens the way for a distinctive account of causality that is simultaneously a form of both empiricism and realism.    

17. References include Rom Harré and Edward Madden, Causal Powers (Totowa, NJ: Rowman and Littlefield, 1974); Ernan McMullin, "Structural Explanation," American Philosophical Quarterly 15 (1978): 139-147, and "Two Ideals of Explanation in Natural Science," Midwest Studies in Philosophy 9 (1984): 205-220; Wesley Salmon, Scientific Explanation and the Causal Structure of the World (Princeton, NJ: Princeton University Press, 1984); Nancy Cartwright, Nature's Capacities and Their Measurement; and Paul Humphreys, The Chances of Explanation (Princeton, NJ: Princeton University Press, 1989).    

18. In just what sense is Aristotelianism a form of empiricism? Rejecting Humean empiricism at every important juncture, Cartwright contrasts her 'empiricism' with what we might call Platonistic rationalism, according to which an acceptable scientific theory need not give a coherent physical picture of its domain as long as it is "a powerful mathematical representation that will work to save the phenomena and to produce very precise predictions" (Nature's Capacities and Their Measurement, p. 5). She goes on to say that certain areas of modern physics, driven as they are mainly by "mathematical considerations and ... not judgments imposed by the phenomena" (p. 6), fail to meet the stringent requirements imposed by an empiricism of this sort.    

Cartwright's view here is at least faintly reminiscent of the standard Thomistic sentiment that the empirical sciences as they are actually practiced are aimed only at securing precise mathematical measurement and not at discovering the nature of physical reality. However, in Chapter 2 of her book Cartwright makes use of historical examples which demonstrate in passing that not all scientists are satisfied with Platonistic rationalism.    

19. The assumption in question goes hand in hand with the claim that at least some instances of singular causality are observable as such. This claim is not usually developed in any detail, though Harré and Madden do argue for it at some length (Causal Powers, pp. 49-67), and medievals such as Aquinas maintained that causality falls into the category of what they called per accidens (or incidental) sensibles.    

20. See, e.g., Cartwright, Nature's Capacities and Their Measurement, p. 36; and Humphreys, The Chances of Explanation, pp. 55-58. Tooley, by the way, claims that those who take singular causation as basic are committed to the possibility that there should be no causal regularities at all. See Causation: A Realist Approach, pp. 175 and 202. I believe that this claim is false or at least in need of careful qualification, but I will not pursue the issue here.    

21. Cartwright comes close to explicitly acknowledging the connection between capacities and teleological explanation when she says, "It is a common--though we think mistaken--assumption about modern physics, for example, that function is not an explanatory feature at all" (Nature's Capacities and Their Measurement, p. 222).    

22. Nature's Capacities and Their Measurement, pp. 181-182.    

23. See Salmon, Scientific Explanation and the Causal Structure of the World, pp. 147 and 155, and Humphreys, The Chances of Explanation, pp. 64-65.    

24. Nature's Capacities and Their Measurement, pp. 142-148.    

25. Nature's Capacities and Their Measurement, p. 166. In "Is Causality Physical?" Midwest Studies in Philosophy 9 (1984): 3-16, Hilary Putnam expresses doubts about the applicability of a distinction between 'real' causes and enabling background condtions:    

If we postulate a "non-Humean caustion" in the physical world, then we are treating causation-as-bringing-about as something built into the physical universe itself: we are saying that the physical universe distinguishes between "bringers-about" and "background conditions." This seems incredible ... Is all this supposed to be "built into" physical reality? The view of those who answer "yes" seems to be a desperate attempt to combine a medieval notion of causation (a notion according to which what is normal, what is an explanation, what is a bringer-about, is all in the essence of things themselves and not at all contributed by our knowledge and interests) with modern materialism. (p. 9)    

Below I will show how Suarez's account of efficient causality draws this important distinction, though I will not in this paper try to deal with Putnam's skepticism about its applicability. Notice, by the way, that one standard objection to J.L. Mackie's analysis of a cause as an INUS condition (an insufficient but non-redundant part of an unnecessary but sufficient condition for the effect) is precisely its inability to draw a sharp metaphysical distinction between 'real' causes and mere background conditions. See Mackie's The Cement of the Universe (Oxford: Clarendon Press, 1974), chap. 3.    

26. Thomism in an Age of Renewal (Notre Dame, IN: University of Notre Dame Press, 1966), p. 8. Indeed, it is probably fair to say that Suarez's metaphysical writings were more influential in Protestant German universities in the seventeenth and early eighteenth centuries than they were in the scholastic revival of the last two centuries.    

27. For a recent extended critique of the claim that events are the basic relata of the causal relation, see Dorothy Emmet, The Effectiveness of Causes (Albany, NY: State University of New York Press, 1985), pp. 6-41. Though Emmet stands squarely within the Aristotelian tradition on this issue, she does express reservations, to be noted shortly, about the Aristotelian notion of substance and its concomitant essentialism.    

28. What I have just said should caution contemporary readers against assuming that substances have all of their accidents contingently rather than necessarily or essentially. According to the scholastics, a substance's inseparable accidents are such that the substance cannot exist without them. The scholastics thus use the term 'accident' in a way different from that in which the term 'accidental property' is normally used in contemporary analytic metaphysics, where an accidental property of a substance is one which the substance has but can lack even while remaining in existence.    

29. For a fine treatment of the dispute over accidents as it bears upon relations, see Mark Henninger, S.J., Relations: Medieval Theories 1250-1325 (Oxford: Oxford University Press, 1989), and for a revealing look at the internal dispute among Thomists over the status of accidental being in St. Thomas's metaphysics, see Barry Brown, Accidental Being: A Study in the Metaphysics of St. Thomas Aquinas (New York: University Press of America, 1985).    

30. The Effectiveness of Causes, p. 77.    

31. The Effectiveness of Causes, pp. 84-85.    

32. Pioneers in this area include, among others, Saul Kripke, "Naming and Necessity," pp. 252-355 in Donald Davidson and Gilbert Harman, eds., The Semantics of Natural Language (Dordrecht: Reidel Publishing Co., 1972); Alvin Plantinga, The Nature of Necessity (Oxford: Clarendon Press, 1974); and Roderick Chisholm, Person and Object (La Salle, IL: Open Court Publishing Co., 1976).    

33. See, e.g., Summa Theologiae I, q. 17, art. 2, response.    

34. DM 17, sect. I, § 6.    

35. ibid.    

36. DM 17, sect. I, § 3.    

37. DM 17, sect. I, § 5. Cartwright uses operation indicators to play the role of designating actions within her formal mathematical representation of causal processes. See Nature's Capacities and Their Measurement, p. 109.    

38. ibid.    

39. DM 17, sect. I, § 5.    

40. Summa Contra Gentiles III, chap. 69.    

41. I have explored this dialectic at some length in "Medieval Aristotelianism and the Case against Secondary Causation in Nature," pp. 74-118 in Thomas V. Morris, ed., Divine and Human Action: Essays in the Metaphysics of Theism (Ithaca, NY: Cornell University Press, 1988).    

42.  "Causes, Causity, and Energy," Midwest Studies in Philosophy 9 (1984), pp. 17-27. The quoted passage is found on p. 22.    

43.  Notice, by the way, that it does not help to reduce all change in nature, as some seventeenth century anti-Aristotelians did, to local motion, i.e., change of spatial position. For the communication of local motion is every bit as mysterious, ontologically speaking, as the communication of qualitative or substantial forms. Malebranche, it seems to me, was exactly right in pointing this out.    

44. DM 17, sect. II, § 2.    

45. Ibid.    

46.  I have briefly explored a few of the relevant issues in "God's General Concurrence: Why Conservation is Not Enough," Philosophical Perspectives 5 (1991): forthcoming. I should add here that divine conservation and divine concurrence are also instances of God's giving esse from the bottom up. However, they are more problematic because they involve (or, in the case of conservation, may involve) the activity of secondary or creaturely causes as well. So I will leave them aside here and refer the reader to the paper just cited for more details.    

47.  Of course, what I have said here presupposes--and thus is not an argument for--the thesis that all finite entities are radically contingent beings whose constituents would all revert to nothingness without a continuing "adequate cause" of their existence. One might, for example, think that the need for an adequate cause applies only to complex beings and not to their elemental physical constituents.    

48.  Of course, the claim that God possesses all possible perfections requires careful unpacking, since there are many formal perfections, e.g., quantitative accidents, which can, strictly speaking, be possessed only by limited or finite beings. Nonetheless, the divine nature is said to contain such perfections "eminently" by virtue of the fact that (i) all such perfections are in some way or other reflective of the divine nature and (ii) God is able to produce all such perfections ex nihilo. Hence, the notion of esse enables St. Thomas to give a clear account of the ontological chasm that separates the transcendent creator of the world from his creatures. What's more, just as each finite entity has its own proper effects, i.e., types of esse or actuality which it can be an immediate "principal" or "perfecting" cause of, so too God as unparticipated esse--esse that is not delimited to any particular species or genus--has his own proper effect, viz., esse-as-such.    

49. DM 18, sect. II, § 2.    

50. DM 17, sect. II, § 17.    

51. The two formulas given here apply to principal and instrumental causes ut quod, but can easily be adapted to apply to causes ut quo.    

52.  Suarez is well aware that in moral philosophy the category of omission is significant. However, on his view omissions are merely 'moral' causes and do not as such involve the giving of esse. He also realizes that within moral philosophy a free agent might be considered a per se moral cause of a given effect even if it is not a per se efficient cause (or what Suarez calls a 'physical cause') of that effect:    

It is always the case that a moral cause is either (i) a cause that does not prevent something when it can and should prevent it, or (ii) a cause that applies a per se cause or induces it, whether by means of advice or by means of entreaties or by way of reward or sometimes even by means of local motion, as when someone applies a fire to a house; for even though he is a per se physical cause of the motion itself, he is nonetheless only a per accidens cause of the burning. But this latter causality, which from a physical point of view is per accidens, is regarded as per se from a moral point of view and by imputation. (DM 17, sect. II, § 6).