Thomas Aquinas, Summa Theologiae

Objection 1: It seems that God is contained in a genus. For a substance is a being that subsists of itself. But this is especially true of God. Therefore God is in a genus of substance.

Objection 2: Further, nothing can be measured save by something of its own genus; as length is measured by length and numbers by number. But God is the measure of all substances, as the Commentator shows (Metaph. x). Therefore God is in the genus of substance.

On the contrary, In the mind, genus is prior to what it contains. But nothing is prior to God either really or mentally. Therefore God is not in any genus.

I answer that, A thing can be in a genus in two ways; either absolutely and properly, as a species contained under a genus; or as being reducible to it, as principles and privations. For example, a point and unity are reduced to the genus of quantity, as its principles; while blindness and all other privations are reduced to the genus of habit. But in neither way is God in a genus. That He cannot be a species of any genus may be shown in three ways. First, because a species is constituted of genus and difference. Now that from which the difference constituting the species is derived, is always related to that from which the genus is derived, as actuality is related to potentiality. For animal is derived from sensitive nature, by concretion as it were, for that is animal, which has a sensitive nature. Rational being, on the other hand, is derived from intellectual nature, because that is rational, which has an intellectual nature, and intelligence is compared to sense, as actuality is to potentiality. The same argument holds good in other things. Hence since in God actuality is not added to potentiality, it is impossible that He should be in any genus as a species. Secondly, since the existence of God is His essence, if God were in any genus, He would be the genus "being", because, since genus is predicated as an essential it refers to the essence of a thing. But the Philosopher has shown (Metaph. iii) that being cannot be a genus, for every genus has differences distinct from its generic essence. Now no difference can exist distinct from being; for non-being cannot be a difference. It follows then that God is not in a genus. Thirdly, because all in one genus agree in the quiddity or essence of the genus which is predicated of them as an essential, but they differ in their existence. For the existence of man and of horse is not the same; as also of this man and that man: thus in every member of a genus, existence and quiddity---i.e. essence---must differ. But in God they do not differ, as shown in the preceding article. Therefore it is plain that God is not in a genus as if He were a species. From this it is also plain that He has no genus nor difference, nor can there be any definition of Him; nor, save through His effects, a demonstration of Him: for a definition is from genus and difference; and the mean of a demonstration is a definition. That God is not in a genus, as reducible to it as its principle, is clear from this, that a principle reducible to any genus does not extend beyond that genus; as, a point is the principle of continuous quantity alone; and unity, of discontinuous quantity. But God is the principle of all being. Therefore He is not contained in any genus as its principle.

Reply to Objection 1: The word substance signifies not only what exists of itself---for existence cannot of itself be a genus, as shown in the body of the article; but, it also signifies an essence that has the property of existing in this way---namely, of existing of itself; this existence, however, is not its essence. Thus it is clear that God is not in the genus of substance.

Reply to Objection 2: This objection turns upon proportionate measure which must be homogeneous with what is measured. Now, God is not a measure proportionate to anything. Still, He is called the measure of all things, in the sense that everything has being only according as it resembles Him.

Articulus 5

Argumentum 1

Ad quintum sic proceditur. Videtur quod deus sit in genere aliquo.

Substantia enim est ens per se subsistens. Hoc autem maxime convenit deo. Ergo deus est in genere substantiae.

Argumentum 2

Praeterea, unumquodque mensuratur per aliquid sui generis; sicut longitudines per longitudinem, et numeri per numerum. Sed deus est mensura omnium substantiarum, ut patet per Commentatorem, X metaphys..

Ergo deus est in genere substantiae.

Sed Contra

Sed contra, genus est prius, secundum intellectum, eo quod in genere continetur. Sed nihil est prius deo, nec secundum rem, nec secundum intellectum. Ergo deus non est in aliquo genere.

Corpus

Respondeo dicendum quod aliquid est in genere dupliciter. Uno modo simpliciter et proprie; sicut species, quae sub genere continentur.

Alio modo, per reductionem, sicut principia et privationes, sicut punctus et unitas reducuntur ad genus quantitatis, sicut principia; caecitas autem, et omnis privatio, reducitur ad genus sui habitus. Neutro autem modo deus est in genere.

Quod enim non possit esse species alicuius generis, tripliciter ostendi potest. Primo quidem, quia species constituitur ex genere et differentia. Semper autem id a quo sumitur differentia constituens speciem, se habet ad illud unde sumitur genus, sicut actus ad potentiam. Animal enim sumitur a natura sensitiva per modum concretionis; hoc enim dicitur animal, quod naturam sensitivam habet, rationale vero sumitur a natura intellectiva, quia rationale est quod naturam intellectivam habet, intellectivum autem comparatur ad sensitivum, sicut actus ad potentiam. Et similiter manifestum est in aliis. Unde, cum in deo non adiungatur potentia actui, impossibile est quod sit in genere tanquam species.

Secundo, quia, cum esse dei sit eius essentia, ut ostensum est, si deus esset in aliquo genere, oporteret quod genus eius esset ens, nam genus significat essentiam rei, cum praedicetur in eo quod quid est.

Ostendit autem philosophus in III metaphys., quod ens non potest esse genus alicuius, omne enim genus habet differentias quae sunt extra essentiam generis; nulla autem differentia posset inveniri, quae esset extra ens; quia non ens non potest esse differentia.

Unde relinquitur quod deus non sit in genere.

Tertio, quia omnia quae sunt in genere uno, communicant in quidditate vel essentia generis, quod praedicatur de eis in eo quod quid est. Differunt autem secundum esse, non enim idem est esse hominis et equi, nec huius hominis et illius hominis.

Et sic oportet quod quaecumque sunt in genere, differant in eis esse et quod quid est, idest essentia. In deo autem non differt, ut ostensum est.

Unde manifestum est quod deus non est in genere sicut species.

Et ex hoc patet quod non habet genus, neque differentias; neque est definitio ipsius; neque demonstratio, nisi per effectum, quia definitio est ex genere et differentia, demonstrationis autem medium est definitio. Quod autem deus non sit in genere per reductionem ut principium, manifestum est ex eo quod principium quod reducitur in aliquod genus, non se extendit ultra genus illud, sicut punctum non est principium nisi quantitatis continuae, et unitas quantitatis discretae. Deus autem est principium totius esse, ut infra ostendetur.

Unde non continetur in aliquo genere sicut principium.

Ad 1

Ad primum ergo dicendum quod substantiae nomen non significat hoc solum quod est per se esse, quia hoc quod est esse, non potest per se esse genus, ut ostensum est.

Sed significat essentiam cui competit sic esse, idest per se esse, quod tamen esse non est ipsa eius essentia. Et sic patet quod deus non est in genere substantiae.

Ad 2

Ad secundum dicendum quod obiectio illa procedit de mensura proportionata, hanc enim oportet esse homogeneam mensurato. Deus autem non est mensura proportionata alicui. Dicitur tamen mensura omnium, ex eo quod unumquodque tantum habet de esse, quantum ei appropinquat.