There are two kinds of knowledge in man arising from two sets of cognitive activity -- the sensory and the intellectual.{1} The latter is of especial importance in arriving at a knowledge of God, so we shall present the stages of intellectual knowledge as found in St. Thomas.
The human intellect is primarily and directly concerned with being in its widest acceptation. More specificially, it is busied with the essence of material things, the universal. This essence as it exists in material things is not in an immediate condition to be known, so there is a power, an intellectual activity, required to make it actually knowable or intelligible. This power is the active intellect, which by its abstractive power immaterializes the corporeal object and brings to light the intelligible species. This species is the likeness of the object in its specific nature; it makes the object actually intelligible and determines the intellect proper to know. This summary statement can now be viewed in its parts.
"What is primarily and per se known by a cognitive power is its proper object."{2} "But being is primarily in the conception of the intellect, for everything is knowable in so far as it is actual . . . Whence being is the proper object of the intellect, and thus it is the first intelligible as sound is the first audible."{3} Being is here taken for actual and possible existence, "it comprehends all the differences and possible species of being, for whatever can exist can be understood."{4} As we are now constituted we are not concerned with all being directly, but with being as found in material things. "The first object of our intellect in our present existence is not being and true of any sort, but being and true viewed in material things, through which we come to a knowledge of all other things."{5} This passage contains the fundamental and oft-repeated truth that we start from material things as a basis and rise gradually to our most immaterial and metaphysical concepts.{6}
The specific or connatural object of the intellect is then the essence of material things. "Through the intellect it is connatural to us to know natures that exist only in individual matter, but not as they are in individual matter but as they are abstracted from it by intellectual consideration. Thus the intellect enables us to know things of this nature as universal. And this is beyond the power of the senses."{7} The intellect deals with the universal which, however, is found in sensible objects, and this power makes it superior to the senses. "Sensitive cognition is occupied with external, sensible qualities, but intellectual knowledge penetrates to the very essence of the thing, for the object of the intellect is the quiddity of a thing."{8} "The proper object proportioned to our intellect is the nature of a sensible thing."{9} This principle rests upon the very nature of man, his relation to matter. The knowable object is proportionate to the knowing power. This power varies according to its connection with matter. Man makes use of a bodily organ in knowing, thus he knows matter, but only what is essential to it reaches his intellect as its proper concept. Essence is intelligible for us only in so far as it is actualized, and it is actualized only in material things. Our mind has a natural tendency to know the intelligible essence, but it reaches it only through sensuous images. "Operation is proportioned to power and essence, but the intellectual in man rests on the sensitive, and thence its proper operation is to understand the intelligible in the phantasmata (images)."{10}
How is the mind to get at the universal, the intelligible in things, for this is its object. This question is answered by the theory of abstraction. The mind possesses a power called active intellect by which it brings in evidence the universal or the intelligible in the thing considered. The existence of such a power, its relation to what is called the passive intellect, its function, and the result of its operation, are all clearly set forth by St. Thomas.
Nothing is changed from the potential to the actual save through something that is actual. Intelligibility requires the object to be actual, individualizing matter is opposed to this knowableness, thus there must be an activity in the mind to draw from material things the essence they contain. This is the active intellect. If universals had an existence independent of matter, as Plato held, then this power would be unnecessary, for its sole purpose is to make actually intelligible the universal existing in material things. This power is then dependent on the doctrine that universals have a fundamentum in re, in things themselves, and must be abstracted before they can become propria of the mind. This power is so necessary that "without it man can understand nothing."{11} Yet it is not of such a nature as to constitute what we might call a distinct mind; it is rather closely associated with the passive intellect. The latter is the intellectual faculty proper -- "the passive intellect is that by which man formally understands,"{12} -- the former is intellectual activity. They are distinct in the sense that we can ascribe different operations to them, but not in the sense of radical separation and totally independent action. "In every act by which man understands, there is the concurrent operation of both active and passive intellects."{13}
The basis for the distinction between these two powers rests on the relation of potency and act in general.{14} The mind is viewed as a passive power, immaterial and destined to know the intelligible, which must be immaterial and intelligible actu before it is an object of intellectual knowledge, "but the intelligible actu is not something existing in rerum natura,"{15} hence there is need of an active power in the mind to bring about this intelligibility and actually account for the knowledge we possess. "The act of the passive intellect is to receive the intelligible, the action or the active intellect is to abstract the intelligible."{16} In discussing the general principles of knowledge, we saw that there was both passivity and activity in the operation of knowing, that both subject and object played a part in effecting knowledge. Here we have the object in the phantasma or imagination acted upon by the active intellect and the result admitted by the passive intellect, as the intelligible in things. "The active intellect is a certain power of the soul extending itself actively to the same things to which the passive intellect extends itself receptively."{17} The former enables the soul to "do all things" (omnia facere), the latter to "become all things" (omnia fieri).
We have said that the purpose of this active intellect is to bring out for the mind the real object existing in material things, to abstract the universal from them. It is an abstractive power and exercises itself solely on the intelligible in sensible things. "Everything is understood in so far as it is abstracted from matter, because the forms in matter are individual forms which the intellect does not apprehend as such."{18} To abstract is to know a thing existing individually in corporeal matter, but not in the manner in which it there exists. "To know what is in such individual matter, but not as it is in such matter, is to abstract the form from individual matter."{19} Knowledge proceeds from the more indeterminate to the less indeterminate, from the imperfect to the perfect, because the intellect is concerned with the universal in the individual. It knows the essence at once as constituent of the thing, and later on by reflection as applicable to many others. The universal is not the result of a comparison between many objects in the sense of the Empiricists, and then recognized as universal because found in many or all, nor is the particular or individual known first by the intellect and then the universal.
The active intellect abstracts the universal from the image in the imagination or phantasia.{20} The image is the instrumental cause in the process, the active intellect is the principal cause. The result partakes of the nature of both causes. Its relation to the image makes it the representation of a specific object, its relation to the active intellect makes it immaterial in nature. We have finally the intelligible species produced in the passive intellect. Sensation from which our knowledge takes its rise is not the full explanation of the universal -- "sensitive cognition is not the total cause of intellectual cognition."{21} Abstraction or the operation of the active intellect simply brings out the universal existing in the given individual object. "One and the same nature which was singular and made individual in each man through matter, afterwards becomes universal through the action of the intellect refining it from individuating conditions.{22}
The active intellect is said to illumine the phantasma, and thus render it fit to arouse the passive intellect to an act of knowledge. Though the phantasmata or images of themselves cannot act on the intellect because they are individual and exist in corporeal organs, yet since they are in the soul which is intellective, they have a special aptitude to become known to the passive intellect through the operation of the active intellect. As the senses receive greater power from their connection with the intellect, so the phantasmata by the power of the active intellect are put in a condition from which the intelligible species can be readily abstracted. This illumination is simply the action of the active intellect, for the latter is not supposed "to imprint anything on the phantasma, but in union with the phantasma it produces the intelligible species in the passive intellect."{23}
The result of the operation of the active intellect is the intelligible species, which is immaterial and represents the thing in its specific nature abstracted from the material object. "What pertains to the specific concept of any material thing, as stone, or man, or horse, can be considered without the individual principles which are not of the concept of the species. And this is to abstract the universal from the particular or the intelligible species from the phantasmata, namely, to consider the nature of the species without considering the individual principles which are represented through the phantasmata."{24} The intelligible species is received in the passive intellect and determines it to know. The intellect is passive, as we have seen, but when stimulated to understand, it is active. What produces the action is related to the intellect as its form, for form is that by which an agent acts. This form is the intelligible species, the intellectual representation of the object known. We might recall here that it is not the species that is known primarily by the mind, but the object it represents; and moreover, the species is of the nature of the knower, and hence does not agree in nature with the physical being of the object. The last stage of the act of knowledge is the mental word, the recognition of the object and the internal expression of this recognition, and this word is "neither the thing itself which is understood, nor is it the very substance of the intellect, but it is a certain likeness conceived in the intellect of the thing which is understood,"{25} and by which we understand the object. This connects us at once with what St. Thomas has to say about the Validity of our Knowledge.
{1} Homo cognoscit diversis viribus cognoscitivis omnia rerum genera, intellectu quidem universalia et immaterialia, sensu singularia et corporalia. Sum. Theol., I, q. 57, a. 2.
{2} Id quod est primo et per se cognitum a virtute cognoscitiva est proprium ejus objectum. Sum. Theol., I, q. 85, a. 7.
{3} Primo autem in conceptione intellectus est ens: quia secundum hoc unumquodque cognoscibile est, in quantum est actu . . . Unde ens est proprium objectum intellectus; et sic est primum intelligibile sicut sonus est primum audibile. Sum. Theol., I, q. 5, a. 2.
{4} Est enim proprium objectum intellectus ens intelligibile, quod quidem comprehendit omnes differentias et species entis possibililis; quidquid esse potest intelligi potest. C.G., 1, 2. c. 98.
{5} Nec primum objectum intellectus nostri secundum praesentem statum est quodlibet ens et verum, sed ens et verum consideratum in rebus materialibus, ex quibus in cognitionem omnium aliorum devenit. Sum. Theol., I, q. 87, a. 3 ad 1.
{6} Proprium autem intellectus est quidquid est in substantia rei. Igitur quidquid intellectus de aliqua re cognoscit, cognoscit per cognitionem substantiae illius rei . . . Cognitio intellectus oritur a sensu . . . Quidquid igitur est in re, quod non potest cognosci per cognitionem substantiae ejus, oportet esse intellectui ignotum. C.G., 1. 3, c. 56.
{7} Unde per intellectum connaturale est nobis cognoscere naturas quae quidem non habent esse nisi in materia individuali; non tamen secundum quod sunt in materia individuali; sed secundum quod abstrahuntur ab ea per considerationem intellectus. Unde secundum intellectum possumus cognoscere hujusmodi res in universali; quod est supra facultatem sensus. Sum. Theol., I, q. 12, a. 4.
{8} Cognitio sensitiva occupatur circa qualitates sensibiles exterioris, cognitio antem intellectiva penetrat usque ad essentiam rei; objectum enim intellectus est quod quid est. Sum. Theol., 22a, q. 8. n. 1.
{9} Proprium objectum intellectui nostro proportionatum, est natura rei sensibilis. Ibid., I, q. 84, a. 7.
{10} Operatio proportionatur virtuti et essentiae; intellectivum autem hominis est in sensitivo et ideo propria ejus est intelligere intelligibilia in phantasmatibus. De Memoria et Reminiscentia, lect. 4.
{11} De Veri., q. 1, a. l ad 3.
{12} De Anima, 1. 3, lect 7.
{13} In omni actu quo homo intelligit, concurrit operatio intellectus agentis et intellectus possibilis De Mente, a. 8, ad 11. Ladd's statement that the power that apprehends the universal is an "intellective soul" is incorrect, and leads him to the following misconception: "This results in a division of the faculties of the soul, which is wholly inconsistent with his (Aquinas') maintenance elsewhere of the true view of the soul as one, but gifted with diverse energies." Phil. of Knowledge, p. 53. St. Thomas never abandons the "true view of the soul as one, but gifted with diverse energies."
{14} "The active and passive intellects are diverse powers, as in all things there is an active and passive power." Sum. Theol., I, q. 79, a. 10. This is the fundamental thought in the Faculty Theory of the Scholastics; the principle itself is very extensive, operating throughout their whole system.
{15} Sum. Theol., I, q. 79, a. 3 ad 3.
{16} Actus intellectus possihilis est recipere intelligibilia; actus intellectus agentis est abstrabere intelligibilia. Q. Dd., De Anima, a. 4 ad 7.
{17} Intellectus agens est . . . virtus quaedam animae ad eadem active se extendens ad quae se extendit intellectus possibilis receptive. Sum. Theol., 1, q. 88, a. 1.
{18} Unumquodque intelligitur in quantum a materia abstrahitur; quia formae in materia sunt individualis formae quas intellectus non apprehendit secundum quod hujusmodi. Ibid., I, q. 50, a. 2.
{19} Cognoscere vero id quod est in materia individuali, non prout est in tali materia, est abstrahere formam a materia individuali. Sum. Theol., I, q. 85, a. 1.
{20} The phantasia for the Scholastics was the faculty that retained the images of absent objects. It is now known as retentive memory.
{21} Sensitiva cognitio non est tota causa intellectualis cognitionis. Sum. Theol., I, q. 84, a. 6.
{22} Una et eadem natura, quae singularis erat et individuata per materiam in singularibus hominibus, efficitur postea universalis per actionem intellectus depurantis ipsam a conditionibus quae sunt hic et nunc. De Universalibus.
{23} The Commentary of the Conimbricenses, De Anima, 1. 3, c. 5, q. 1, a. 3 ad 1.
{24} Ea quae pertinent ad rationem speciei cujuslibet rei materialis, puta lapidis, aut hominiis, aut equi possunt considerari sine principiis individualibus, quae non sunt de ratione speciei. Et hoc est abstrahere universale a particulari, vel speciem intelligibilem a phantasmatibus, considerari scilicet naturam speciei aliaque consideratione individualium principiorum, quae per phantasmata repraesentantur. Sum. Theol., 1, q. 85, a. 1 ad 1.
{25} C.G., l. 4, c. 11.