Thomas Aquinas

“ Further, the intellect is true in its act of understanding. But truth, being a certain equality between thought and thing, is not subject to more or less; for a thing cannot be said to be more or less equal. ”

“ But to know distinctly what is contained in the universal whole is to know the less common, as to "animal" indistinctly is to know it as "animal"; whereas to know "animal" distinctly is know it as "rational" or "irrational animal," that is, to know a man or a lion: therefore our intellect knows "animal" before it knows man; and the same reason holds in comparing any more universal idea with the less universal. ”

“ For it is quite true that the mode of understanding, in one who understands, is not the same as the mode of a thing in existing: since the thing understood is immaterially in the one who understands, according to the mode of the intellect, and not materially, according to the mode of a material thing. ”

“ I answer that, The Philosopher (De Anima iii, 6) compares intellect with sense on this point. For sense is not deceived in its proper object, as sight in regard to color; has accidentally through some hindrance occurring to the sensile organ---for example, the taste of a fever-stricken person judges a sweet thing to be bitter, through his tongue being vitiated by ill humors. Sense, however, may be deceived as regards common sensible objects, as size or figure; when, for example, it judges the sun to be only a foot in diameter, whereas in reality it exceeds the earth in size. ”

“ But according to Plato, who held that universals are subsistent, the universal considered thus would be prior to the particular, for the latter, according to him, are mere participations of the subsistent universals which he called ideas.
Secondly, the universal can be considered in the nature itself---for instance, animality or humanity as existing in the individual. And thus we must distinguish two orders of nature: one, by way of generation and time; and thus the imperfect and the potential come first. In this way the more common comes first in the order of nature ”

“ Further, the intellect is the most formal of all that is in man. But different forms cause different species. Therefore if one man understands better than another, it would seem that they do not belong to the same species.
On the contrary, Experience shows that some understand more profoundly than do others; as one who carries a conclusion to its first principles and ultimate causes understands it better than the one who reduces it only to its proximate causes. ”

“ I answer that, The human intellect must of necessity understand by composition and division. For since the intellect passes from potentiality to act, it has a likeness to things which are generated, which do not attain to perfection all at once but acquire it by degrees: so likewise the human intellect does not acquire perfect knowledge by the first act of apprehension; but it first apprehends something about its object, such as its quiddity, and this is its first and proper object ”

“ On the contrary, The intelligible species is to the intellect what the sensible image is to the sense. But the sensible image is not what is perceived, but rather that by which sense perceives. Therefore the intelligible species is not what is actually understood, but that by which the intellect understands. ”

“ First, that intellectual knowledge in some degree arises from sensible knowledge: and, because sense has singular and individual things for its object, and intellect has the universal for its object, it follows that our knowledge of the former comes before our knowledge of the latter. ”

“ Some have thought that the species of a natural thing is a form only, and that matter is not part of the species. If that were so, matter would not enter into the definition of natural things. Therefore it must be said otherwise, that matter is twofold, common, and "signate" or individual; common, such as flesh and bone; and individual, as this flesh and these bones. The intellect therefore abstracts the species of a natural thing from the individual sensible matter, but not from the common sensible matter ”

“ The same applies to the intellect in two ways. First, as regards the intellect itself, which is more perfect. For it is plain that the better the disposition of a body, the better the soul allotted to it; which clearly appears in things of different species: and the reason thereof is that act and form are received into matter according to matter's capacity: thus because some men have bodies of better disposition, their souls have a greater power of understanding, wherefore it is said (De Anima ii, 9) , that "it is to be observed that those who have soft flesh are of apt mind." ”

“ Secondly, we must consider that our intellect proceeds from a state of potentiality to a state of actuality; and every power thus proceeding from potentiality to actuality comes first to an incomplete act, which is the medium between potentiality and actuality, before accomplishing the perfect act. The perfect act of the intellect is complete knowledge, when the object is distinctly and determinately known ”

“ Hence it is clear that there is a perfect understanding, than which none other is more perfect: and therefore there are not infinite degrees of understanding a thing: nor can one person understand a thing better than another can. ”

“ Not only does the active intellect throw light on the phantasm: it does more; by its own power it abstracts the intelligible species from the phantasm. It throws light on the phantasm, because, just as the sensitive part acquires a greater power by its conjunction with the intellectual part, so by the power of the active intellect the phantasms are made more fit for the abstraction therefrom of intelligible intentions. ”

“ Now all intelligible species belong to one genus, because they are the perfections of one intellectual faculty: although the things which the species represent belong to different genera. Therefore it is impossible for one and the same intellect to be perfected at the same time by different intelligible species so as actually to understand different things. ”

“ There is another grade of cognitive power which is neither the act of a corporeal organ, nor in any way connected with corporeal matter; such is the angelic intellect, the object of whose cognitive power is therefore a form existing apart from matter: for though angels know material things, yet they do not know them save in something immaterial, namely, either in themselves or in God. But the human intellect holds a middle place: for it is not the act of an organ ”

“ One, in regard of impression only, and thus the operation of the senses takes place by the senses being impressed by the sensible. The other is formation, inasmuch as the imagination forms for itself an image of an absent thing, or even of something never seen. Both of these operations are found in the intellect. ”

“ The likeness through which we understand is the species of the known in the knower; therefore a thing is known first, not on account of its natural likeness to the cognitive power, but on account of the power's aptitude for the object: otherwise sight would perceive hearing rather than color. ”

“ Mathematical species, however, can be abstracted by the intellect from sensible matter, not only from individual, but also from common matter; not from common intelligible matter, but only from individual matter. For sensible matter is corporeal matter as subject to sensible qualities, such as being cold or hot, hard or soft, and the like: while intelligible matter is substance as subject to quantity. ”

“ Neither is it necessary that, as regards us, knowledge of any cause or principle should be secondary: since at times through sensible causes we become acquainted with unknown effects, and sometimes conversely. ”

“ The intellect is above that time, which is the measure of the movement of corporeal things. But the multitude itself of intelligible species causes a certain vicissitude of intelligible operations, according as one operation succeeds another. ”