Summa contra Gentiles3.41 Chapter XLI. Is it possible for man, in this life, to understand separate substances by the study and inquiry of speculative sciences?

The intellectual substance has yet another knowledge of God. For we have said in the Second Book’ that the separate intellectual substance, by knowing its own essence, knows both what is above it, and what is below it, in a way proportionate to its substance. This must especially be the case, if that which is above it, be its cause, since the likeness to the cause must be found in the effect. Wherefore, since God is the cause of all created intellectual substances, as proved above,” it follows that separate intellectual substances, by knowing their own essence, know God Himself by the way of some kind of vision: for the intellect knows by the way of vision the thing whose likeness is in the intellect; just as the likeness of the thing seen by the body, is in the sense of the seer. Whatever intellect, therefore, apprehends a separate substance, by knowing what it 1s, sees God in a higher way than he is known by any of the kinds of knowledge mentioned above. Accordingly, whereas some have deemed man’s ultimate happiness to be in this life, for the reason that he knows separate substances, we must inquire whether in this life man be able to know separate substances: and it is a point that may well be questioned. For our intellect, according to its present state, understands nothing without a phantasm, which stands in the same relation to the possible intellect, whereby we understand, as colours to the sight, as was made clear in the Second Book. Hence if, through the intellectual knowledge which is acquired from phantasms, it be possible for any of us to succeed in understanding separate substances, it will be possible in this life for someone to understand these same separate substances; and in consequence, by seeing these separate substances, he will participate in that mode of knowledge with which the separate substance, by understanding itself, understands God. If, on the other hand, by knowledge derived from phantasms, it be altogether unable to succeed in understanding separate substances, it will be impossible for man in the present state of life to acquire the above mode of divine knowledge.

The possibility of succeeding in understanding separate substances, through knowledge derived from phantasms, has been explained by some in various ways. Avempace' maintained that by the study of speculative sciences, it is possible to arrive at a knowledge of separate substances, from understanding those things which we know through phantasms. For we are able by the action of the intellect to extract the quiddity of a thing which has quiddity without being its quiddity. Because the intellect is naturally adapted to know any quiddity as such: since the proper object of the intellect is what/a thing is. Now if that which is first understood by the possible intellect is something that has a quiddity, we can, by the possible intellect, abstract the quiddity of the thing first understood; and if this quiddity has again a quiddity, it will be again possible to abstract the quiddity of this quiddity. And since we cannot go on indefinitely, we must stop somewhere. Therefore by way of analysis our intellect can arrive at knowing a quiddity that has no quiddity: and such is the quiddity of a separate substance. Consequently, through its knowledge of these sensibles, that is acquired from phantasms, our intellect can arrive at understanding separate substances.

He goes on to prove the same statement by another yet similar way. Thus, he lays down that the idea of a thing, for instance of a horse, in me and in you is multiplied only through the multiplication of the spiritual forms, which are different in you and me. It follows then that an idea which is not clothed with any such form, is the same in you and me. Now, as we have proved, the quiddity of the idea, which our intellect by its innate aptitude abstracts, has no spiritual and individual form: for the quiddity of the idea is not the quiddity of the individual, whether corporeal or spiritual, since the thing understood, as such, is universal. Therefore our intellect has a natural aptitude to understand a quiddity the idea of which is the same in all. Such is the quiddity of a separate substance. Therefore our intellect has a natural aptitude to know separate substances.

Yet, if we consider the matter carefully, these explanations are frivolous. For since the idea as such is universal, the quiddity of an idea must be the quiddity of a universal, namely genus or species. Now the quiddity of the genus or species of these sensible objects, the intellective knowledge whereof we acquire through phantasms, includes both matter and form. Consequently it is quite unlike the quiddity of a separate substance, which is simple and immaterial. Therefore it is impossible to understand the quiddity of a separate substance, through understanding the quiddity of a sensible object.

Again. A form that cannot as to its very being be separated from a particular subject.is not of the same kind as a form which, in its being, is separated from a particular subject, although both may be considered apart from that particular subject. For magnitude is not the same kind of thing as a separate substance, unless we suppose there are separated magnitudes midway between the species and the sensible object, as some Platonists have maintained. But the quiddity of a genus or species of sensible things cannot be separated in its very being, from a particular individual matter; unless perhaps, as the Platonists think, we suppose the species of things to exist separately, which Aristotle has refuted. Consequently the aforesaid quiddity is altogether different from separate substances, which are nowise in matter. Therefore it does not follow from the fact that these quiddities are understood, that separate substances can be understood.

Moreover. If we grant that the quiddity of a separate substance is of the same kind as the quiddity of the genus or the same specific kind, unless we say that the species of about separate substances except their remote genus. Now by knowing the genus, we do not therefore know the species understand a separate substance through understanding the quiddities of these sensible things.

Besides. A separate substance differs more from sensible things, than one sensible from another. But understanding the quiddity of one sensible does not suffice for understanding the quiddity of another: for a man who is born blind, is quite unable through understanding the quiddity of sound, to Further. Ifagain we grant that the spheres of the separate substance are causes of movement, and that by their moveof knowing separate substances through sensible things, does effect we know its cause either in the point of likeness between cause and effect, or in this, that the effect indicates the power of the cause. In the point of likeness, we do not gather from the effect what the cause 1s, unless agent and effect be of one species: and this is not the case with separate substances and sensible things. In the point of power, it is again impossible unless the effect equal the power of the cause: since then the whole power of the cause is known from the effect; and the power of a thing indicates its substance. But this cannot apply to the point in question: because the powers of separate substances surpass all the 1 Ch, xxii. seq.

sensible effects that our intellect understands, even as a universal power surpasses a particular effect. It is therefore impossible through understanding sensible objects to arrive at understanding separate substances.

Moreover. Whatever intelligible things we are able to know by means of inquiry and study, belong to one or other of the speculative sciences. Accordingly if through understanding the natures and quiddities of these sensible objects, we succeed in understanding separate substances, it follows that it would be possible to understand separate substances through one or the other speculative science. Yet we do not find this to be the case: for no speculative science teaches what any separate substance is, but only the fact that it is. It is therefore not possible to succeed in understanding separate substances through understanding the natures of sensible objects. And if it be said that sucha speculative science is possible, although it has not yet been discovered, this makes no difference, since it is not possible, from any principles known to us, to arrive at understanding the aforesaid substances. Because all the proper principles of any science whatever, depend on the first indemonstrable self-evident principles, the knowledge of which we acquire from sensible objects, as stated in 2 Postey.xv. And sensible objects do not sufficiently lead to the knowledge of immaterial things, as we have proved in the preceding arguments. Therefore no science is possible whereby one may be able to attain to the understanding of separate substances.