Jacques Maritain Center : The First Principles of Knowledge

Chapter XIII.
Evidence as the Ultimate Objective Criterion of Truth.


  1. The nature of human knowledge, and the consequent nature of its objective criterion.
  2. We have to show that this is evidence. What we mean by evidence.
  3. Proof that evidence is the ultimate objective criterion.
  4. Confirmation of the proof from animal instinct.
  5. A series of objections, serving to bring out more clearly the meaning of evidence as a criterion. (a) The criterion of evidence means judgment by appearances. (b) The criterion is tautological, "that is certain which is evident;" whereas we want a rule to settle what in every case is evident -- not a declaration that the evident, when found, is the true. (c) How can abstract truths, and truths about mere possibilities have an objective reality, when they exist only as terms of the mind?
  6. The complicated nature of evidence.


OFTEN because they have expected too much from a universal criterion of truth, philosophers have declared that no such thing is possible. While some affirm that there are innumerable criteria for different cases, but no common criterion for all, others have gone further and proclaimed absolute certainty to be beyond human attainment. The question is undoubtedly difficult; and yet difficulties will yield to a patient examination of what it is we experience when we have these states of certainty, which previous propositions have shown to be sometimes ours.

I. The subject of a criterion has so many ramifications, that we must pick out what part precisely of the problem is to occupy our attention. And first it will be well to quote the very words of some of the schoolmen, in which they describe the process of knowing, and therefore the process of acquiring certitude, as involving acts of conception.

The schoolmen, to show that knowledge is no mere subjective fact, insist upon its origin in us by way of a conception and birth, and of double parentage.{1} Knowledge is generated by subject and object together: "Whatever object we know, this in union with the cognitive faculty generates within us the knowledge of itself. For knowledge is equally the product of both. Hence when the mind is conscious of itself, it is the sole parent of its self-knowledge being at once the knowing and the object known."{2} The union of object with subject must be brought about "either by means of its own essence or by a similarity between. them."{3} Thus teaches St. Thomas. In the same sense is the reaching of Suarez: "The cognitive power is in a state of indetermination as regards the production of this or the other object: hence to be determined to a particular act of knowledge, it needs to be placed in a certain relation with the object."{4} In the same way Silvester Maurus argues, that knowledge must be the joint product of faculty and object: as a vital, assimilative act it must be the work of the intellect; but for its determination to one definite similitude rather than to another it must be dependent on the object.

This doctrine, that human knowledge results from faculty as determined by object would be simple enough, if the intellectual object could be shown always to work upon the intellect, as a luminous body upon the eye. But an appeal to examples shows that the case is otherwise. According to St. Thomas and the Thomists, it is truer to say that, the intellect illuminates its object than that the object illuminates the intellect; evidence does not simply pour in upon the mind from outer things, but the intellect has rather to furnish its own light of evidence. Hence Lepidi writes: "The criterion whereby the mind judges is the faculty of judging; the criterion according to which it judges, is the rule or norm of truth, in other words, that inner light whereby an object becomes evident."{5} He further adds: "This light has, so to speak, two aspects, one, in so far as it is in the soul which it informs and perfects ; the other, inasmuch as it actually represents the object outside the mind."{6} The first aspect he calls subjective, the second objective: but what may disappoint the reader is, that this objective aspect seems really part of the subjective light, not an influence, an irradiation, a determination coming from the object. If only thought could be described as the direct reaction of the faculty under a directly intelligible impression from the object, it would be satisfactory: whereas, besides its own intrinsic difficulties, the scholastic account of how material bodies are brought to bear on the determination of thought about themselves, seems to deny all real action of such bodies on the mind. The problem is confessedly difficult,{7} and has been assigned, not to the logical, but to the psychological division of treatises in the scholastic system.

Having stated there the deeper difficulty lies, we may proceed to do enough for the establishment of an objective criterion of truth within the limits of our own treatises.{8}

The criterion, quo fit judicium, is clearly the intellect itself, and this we suppose given: but the objective criterion, secundum quod fit judicium, this in its ultimate and universal nature is what we have to investigate.

Now we shall avoid the difficulties above signalized, if we take the problem up at a stage to which all must admit that it advances, however they may dispute as to the means of this advance. All certitudes concern propositions, and, in last resort, propositions are to be decided, not by inference from others, but on their own merits. Our inquiry into an ultimate objective criterion may take this shape: What, in last analysis, is the objective character of all those propositions, which, when they come before the mind for judgment, claim from it, for their own sake, a firm assent? This character will be the criterium secundum quod of which we are in search.

2. It may be declared at once that evidence is the objective character, quality, or property which we seek: but since the manner of this is not obvious at once, we must have the courage to plunge into details. Evidentia is the Latin word used by Cicero{9} for enargeia, the root of which is found also in argumentum, &c.{10} The radical meaning therefore is to make clear, bright, distinct, conspicuous. Everything, actual or possible, as is proved in General Metaphysics, has its truth -- its ontological truth; and the manifestation, or shining forth of this, is called evidence. Hence the speculation as to whether there are, perhaps, things-in-themselves, which have no relation whatever to any intelligence, is philosophically absurd. Ontological truth is co-extensive with all being, and whatever makes this truth apparent to the mind gives its evidence. Not all things are evident to us, or our ignorance would not be what it is: still several things do become to us immediately or mediately evident; and when we speak thus, we are using the word evident not in its popular use for what is easily perceptible, but in its technical use for what is perceptible, whether by easy or by difficult means.

Evidence, therefore, is that character, or quality, about proposed truths or propositions, whereby they make themselves accepted by the intellect, or win assent; while the intellect is made conscious, that such assents are not mere subjective phenomena of its own, but concern facts and principles, which have a validity independent of its perception of them. In saying, then, that evidence is the ultimate criterion, we are implying, that the criterion is not, as some have vainly imagined, an all-containing proposition, from which any other truth may be evolved; further, that is not a proposition at all, but a character of all propositions which so come before the mind, as rightly and for their own sake to demand its assent. When the nature of this character has been discovered, of course it may be declared in a proposition, or enunciated as a principle, "Evidence is the criterion of truth." But the criterion in itself is not a proposition or principle: it is a quality found in all propositions or principles which we can rationally accept, for their own sake, and is the reason of that acceptance.

3. To prove now that there is an objective evidence, which experience tells us to be our ultimate criterion. It is taught in theology that God is the substantial truth and always knows all truth. He does not gradually arrive at His knowledge by the use of faculties determined in their activities by outer agents; eternally and immutably He has all knowledge, without increase or diminution.

But we are beings that start with no knowledge, and gradually acquire our stock by passing de potentia in actum, from potentiality to act. Moreover, this transition is not effected by mere internal evolution; the faculties must be roused and determined by something other than themselves. Each faculty has it own proper excitant to wbich alone it is responsive. The ear responds only to one generic mode of outer vibration, the eye only to another, the palate only to what seems to be a definite kind of chemical process. and so on with regard to the other senses. Our finite intellect, in like manner, responds only to some appropriate character on the side of the objects presented to it, whatever be the way in which that presentation is effected. Now this character is what we call objective evidence, because the term accurately describes the state of things revealed by the careful consideration of our own experience. Surely it is right to frame our theory on the analysis of experience: and what it teaches is, that we do not make truth, but take it, when it urges itself upon us in a certain way, such that we feel it to be something independent of us, existing before us, and giving the law imperiously to our course of thought. Consider the proposition: "Nothing can arise by chance, everything must have a sufficient reason." In viewing the terms here, we feel that the relation between them forces itself upon us by way of objective evidence: we as distinctly feel the pressure put upon intelligence by some reality other than itself, as we feel on our bodily organs the pressure of an external weight.{11} Of course we may view the case on the subjective side, and say that it is insight which carries us along. True, but insight must have its obiect, and must feel the influence of that object. Mere subjectivism would never so distinctly objectivize itself, never tell us so plainly that the truth we contemplate is valid for all intelligence, and that to no intelligence can it really be manifest, as a truth for it, that events may happen without an adequately efficient cause. Objective evidence must here lend its aid.

The argument will not avail unless we recall the doctrines already laid down about necessary truth, and about the first condition of philosophizing, which is our assumed ability to reach objective truth. But with these doctrines in mind, we shall be forced to admit the fairness of the analysis, which, from an experienced act of certitude, disengages objective evidence as the element forming the criterion. Those who deny such an element, or who deny to it its right position, will be found denying necessary truth and violating the first condition of philosophy, as also asserting principles which lead directly to universal scepticism. Thus they violate the implied agreement of all intelligent discussion, that whoever in the course of it enunciates principles which are the subversion of all rational disputation, should be thereby declared to have sufficiently refuted himself, and to be silenced for the future.

4. The proof that objective evidence is man's criterion of truth gains some confirmation from a contrast with animal intelligence. It is the commonly admitted opinion, that, whatever may be the process of animal instinct, it is not one of calculated means and ends. If the bee does build what is mechanically the best sort of cell, it is not because of perceived mathematical relations, nor because of the perceived fitness. Thus the process, by its contrast with our way of deliberately adapting means to ends, serves to bring out more clearly our mode of thought, and to emphasize the criterion of objective evidence.

5. The meaning of evidence as a criterion will be brought out into still greater clearness, if we run through a series of objections against the term and its use.

(a) First, it may be said to sanction a habit of judging by mere appearances, on the maxim, "That is evident which to me appears to be,"{12} yet the sounder maxim is, "Trust not appearances." In answer, we reply that appearances always are what, under the circumstances, they ought to be, if we except moral deception on the part of a free agent; so that it is not the appearances which are false, but our erroneous interpretation of them. In a sound sense we may give the advice, "Judge by appearances," for they are all you have got to judge by; and they are always the manifestation of some truth, with the exception just mentioned. By evidence, however, we do not mean sensible manifestation alone.

(b) From a charge of deceptiveness we pass to a charge of futility or tautology. "Where is the use," says an opponent," of settling that the evident must be accepted as true? Of course it must; but the criterion we want is one which shall tell us, in all cases, what is evident." We answer that such a criterion cannot be found, or logic would be the sole science pointing out in every instance where truth lies. The logical criterion, which takes the form of the highest generality, cannot discharge this office of omniscience. Yet the function it does discharge is useful. When logic says, Objective evidence is the criterion of truth, it does not leave the words unexplained: else they might convey to the bearer no more than a truism: but it makes them the outcome of an analysis of the act of certitude; and thus they receive a fulness of meaning, which redeems them from tautology.

(c) "Be it so," rejoins our opponent; "but at any rate that is wholly subjective which is wholly in the mind; now truths about mere possibilities are wholly in the mind, and all abstract, universal truths formally exist only as terms of the mind. They are truths in the mind, but where is the objective evidence, or outer reality to which mind conforms?" The only reply to the first part of this difficulty is got by borrowing the results of a distinct section in General Metaphysics; in which it is proved, that possibilities are not mere nothings, nor mere mental terms, but have a real foundation at least in the nature of the Supreme Being, and often more proximately in some actually created nature. Each of them has an ens essentiae, though not an ens existentiae. As to the second part of the proposed difficulty, the reality attributable to abstract or universalised truths will be proved later. That there is some reality in possibilities and generalized science every one must feel, however much he may be unable distinctly to formulate to himself wherein it consists. Still the mere unformulated persuasion ought to induce the pure empiricist to distrust his position, which will not allow him to regard science as real in the laws which it lays down.

6. A further difficulty stands over in the fact, that what we speak of under the one simple name of evidence, enters into concrete cases after a very complicated way, and is far from being one simple thing. We must distinguish different evidences. Evidence is sometimes immediate, and then it presents no difficulty: but sometimes it is mediate, and the steps of inference may be many and intricate. Both mediate and immediate evidence may be intrinsic to the case considered, as in the most abstruse mathematical theorem: but sometimes the evidence is extrinsic to the truth acquiesced in, as in the case where an ignorant man accepts a scientific conclusion, not from any insight into how it was derived, but from the evidence he has of the trustworthiness of his informant.

Again, the way in which what we call "the evidence" for a case is made up of several evidences in detail, some of which tend in opposite directions, is instructive as to the meaning of the term. Suppose a man charged with murder; the items for the defence being (a) that the prisoner had no discoverable motive for the crime; (b) that his previous conduct gave no serious indication of a character likely to be guilty of excessive violence: (c) that there exists another man likely enough a priori to have committed the crime, but quite free from any demonstrable connexion with it: and the items for the prosecution being, (a) that the prisoner, and only he, can be shown to have been near the spot about the time of the murder: (b) that there was a blood stain on his clothes: (c) that the weapon used was a dagger, and he possessed a weapon of that kind, which he says he parted with months ago.

Here let us speak of the evidences, rather than the evidence. First, they consist of the arguments which fully prove, as we will suppose, the respective three statements, pro and con: thus we have six separate certitudes. The difficulty begins when out of these we try to derive a seventh, namely, the guilt or the innocence of the man. At once we get into the region of probabilities, the very character of which is that full evidence is wanting, and we are left to conjecture beyond the reach of proof. It is precisely the probabilities which point to contradictory conclusions: the evidences, strictly so-called, cannot conflict. for so far as there is evidence there is truth, and no truth can gainsay another truth. There is some way of reconciling all apparent conflict, though we may not be able to find it out. Advertence to complications like these, while it clears up our ideas about the practical use of evidence, takes away all misgiving from the circiiinstance, that in spite of our having an infallible criterion, we are yet fallible judges, who blunder oftentimes. Evidence is safe where it is sufficiently abundant and direct to the point: but evidence, scarce and indirect, may very well prove a fallacious means when employed by creatures such as we are. But of this in the next chapter. Here it only remains to add, in conclusion, that unsolved difficulties do not destroy a certitude once fully established; for probabilities disappear before a contrary certainty, no matter how preponderant their weight may have been as probabilities. If the highest probability were beyond all fear of a failure, it would be certainty, and riot probability.


(I) Some schoolmen, besides the wider sense of evidence, use a narrower sense, according to which that only is evident, which has necessitating evidence, making the truth so clear that the mind cannot well refuse assent. Such evidence does not exist in some instances, where an element of good will is requisite for arriving at the right conclusion. In this sense we hear of propositions being certain, but not evident.

(2) The schoolmen describe material objects as being in themselves not immediately intelligible: hence they deny that a material object can efficiently act on the mind; and many carry this denial even as far as to include under it mediate action through the sense-image in the brain. Hence a long discussion about the illuminatio phantasmatis and the production of a species intelligibilis. The matter must be left to psychology; but it so closely bears on the thesis about objective evidence, that to fail of noticing the near connexion would hardly be right. At any rate we can always insist that intellect, be its object material or not, is guided by objective law, not by mere subjective evolution, independent of an object; and that the senses have a demonstrative influence on the objective side. We need not, therefore, call in any mystical theory, such as that apparently suggested in Mr. Wylde's Physics and Philosophy of the Senses, where we read, that ,the whole of our intercourse with nature is literally the connexion of mind with mind, between the Great Mind and the mind of His creatures, not by miraculous means, but by and through the operation of those ordinary laws, of which He is the present and sustaining principle." lf this means only that God sustains and cooperates with all secondary agencies, it is correct; but if it implies that secondary agencies are not adequately operative in their own manifestation, it is erroneous.

(3) The criterion is laid down for our ordinary knowledge, not for any supernatural or preternatural communications. Neither does it concern those things which must, in part at least, be matters of personal taste, without an absolute objective standard, such as the choice between two recognized styles of architecture, of music, or of painting. Preferences in these matters must be largely referable to subjective conditions; and the extravagance is, when a man insists on making his own private likings a law for others, who are just as competent to decide for themselves. The misery is, that so many people, especially in matters of variable taste, are so insistent upon an invariable conformity to their favourite standard, which has no valid claim to be exclusive. Because the matters are so little to be fixed by argument, therefore strength of assertion is called in to supply for proof.

(4) A curious phenomenon of imagination or emotion which some seem to mistake for a failure of intelligence, is exhibited in cases where men, out of fear, will not act when reason clearly tells them it is safe to act. Thus some will go to great trouble rather than step over a serpent, which they know to be dead; others cannot be persuaded to take an eel off a fish-hook, on account of its likeness to a serpent; and others will not go near a corpse, which they are intellectually convinced will do them no harm. At least these examples do not diminish the rank of evidence as a criterion for assents of the mind, whatever they may do against man's character for reasonable conduct.

{1} Cf. Kleutgen, Philosophie der Vorzeit, I. § 22.

{2} "Omnis res, quamcumque cognoscimus, congenerat in nobis notitiam sui. Ab utroque enim notitia paritur, a cognoscente et cognito. Itaque mens, cum seipsam cognoscit, sola parens est notitiae sui; et cognitum enim et cognitor ipsa est." (St. Thomas De Trinit., 1. ix.c. xii.)

{3} "Sive per essentiam suam sive per similitudinem." (Idem, De Veritate, q. viii. a. 6.)

{4} "Potentia cognoscitiva est indifferens ad operandum circa hoc vel illud objecum; et ideo, ut determinetur in particulari ad cognoscendum, indiget conjunctione aliqua ad ipsum objectum." (De Anima, 1. iii. c. i.)

{5} "Criterium per quod intellectus judicat est ipsa facultas judicandi: criterium secundum quod, est ipsa regula vel norma veri, nempe lux illa interior, secundum quam res manifestatur." (Logica p. 236.)

{6} "Habet haec lux, ut ita dicam duas facies, unam quatenus est in anima, quam informat et perficit; alteram quatenus rem extra animam actu repraesentat ac refert." (Logica, p. 361.)

{7} Kleutgen, ut supra.

{8} What the need of this criterion is, will the more manifestly appear, if we look into the writings of some of those authors, who not being downright Kantians, are considerably under the influence of Kant's doctrine that we must inquire rather how objects conform themselves to mind, than how mind conforms itself to objects, and that there are a priori forms of mind, such as substance and accident, causality and dependence, which for aught we can know, may have no validity except as conditions of our thought. Such a doctrine is ruinous to objective knowledge and is too much favoured by Mansel (Prolegomena Logica, c. iii. p. 77), who tells us, that "the aws to which our faculties are subjected, though perhaps not absolutely binding on things in themselves, are binding upon our mode of contemplating them." When we hear such language we are prompted to seek an objective criterion, which at the same time shall be consistent with the subjective law, cognitum est in cognoscente ad modum cognoscentis.

{9} Academ. Lib. II. c. vi. n. 17. (Nobbe's Edition.)

{10} "Nihil clarius enargeia, ut Graeci perspicuitatem, aut evidentiam nos, si placet, nominemus."

{11} This is the idea which Locke, with no great success, tries to bring out in answer to his own question, how do men know that their ideas really represent the conditions of things? "Simple ideas," he replies "since the mind can by no means make them to itself, must necessarily be the product of things operating on the mind in a natural way, and producing therein those perceptions, which by the wisdom of our Maker they are ordained to." (Human Understanding, Bk. IV. c. iv. § 4.) He adds that simple ideas "carry with them all the conformity which is intended, or which our state requires, for they represent to us things under those appearances which they are filled to produce in us." Words like these last convey to many readers the impression that Locke regarded knowledge too much after the manner of the passive reception of a stamp inpressed on the faculties by outer agents; and he is certainly unsatisfactory in what he teaches elsewhere in the same book. (c. ii. § 14.) Here he asserts our knowledge of the outer physical universe to be beyond "bare probability," yet not equal to "intuition" and "demonstration." If he meant no more than that physical certitude is of a lower order than metaphysical, he would have been right enough: but he seems to allow the possibility that the former may not be a full certitude: "There can be nothing more certain than that the idea we receive from an external object is in our minds: this is intuitive knowledge. But whether there be anything more than barely an idea in our minds, whether we can thence certainly infer the existence of anything without us which corresponds to that idea, is that whereof some men think that there may be a question made because men may have such ideas in their minds when no such thing exists, no such object affects their senses."

{12} "Evidens est quod videtur."

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