Commentaria in Summam contra Gentiles, Liber II

From what has been laid down it follows ¹, that God, although omnipotent, cannot do certain things.

I. For from the fact that it has been shown that there is in it no passive potency, it follows that it cannot have those things that belong to passive potency, such as the capacity that pertains to esse. For it cannot be a body or anything of this kind. Nor can it be changed; nor fail and be corrupted; nor grow weary or forget; nor be overcome or suffer violence; nor repent, or be angry, or grieve.

From the fact that it has been shown that in it there is active power, and that the object of active power is being made, it follows that it cannot do what is against the account of being as being or against the account of the made as made; for no power can act where the account of its object is lacking. On account of the deficiency of being, it cannot make that the same thing be and not be at once; that opposites be together in the same thing according to the same respect; that a thing lack something of its essential principles, as that a man not have a soul; that genus not be predicable of species; that lines drawn from center to circumference not be equal; that a rectilinear triangle not have three angles equal to two right angles; that what is past not be past; and similar things which are repugnant to the account of being. — But on account of the deficiency of being made, it cannot make God, or anything equal to itself, or that anything be conserved without itself. For all these things are against the account of the made.

From this too, since it has been shown that He acts through His will, it follows that He cannot do what He cannot will. And thus He cannot make Himself not to be, or not be good or blessed. Similarly, He cannot sin. But from the fact that it has been shown that God's will is immutable, it follows that He cannot fail to bring about what He has willed from Himself. — Yet Saint Thomas notes that this inability is understood in a different way than the preceding ones. For those things He can neither will nor do simply; but things of this kind He can both will and do absolutely, though not supposing a will for the opposite. Hence, when it is said, God cannot do the contrary of what He has disposed Himself to do, this must be understood in the composite sense, implying, namely, the disposition of the divine will for the opposite: but not in the divided sense, as though they were considered with respect to the divine power and will taken absolutely.

Similarly, because it has been shown that he acts through knowledge, therefore he cannot do what he did not foreknow himself would do, or omit what he foreknew himself would do: understanding this, however, not absolutely, but under a condition or supposition.

II. Concerning the past, a doubt arises that must not be concealed. For it is established that pastness is an accident of a thing per accidens. But God can bring about any thing without that which belongs to it per accidens. Therefore God can bring about a thing that has passed away without its pastness. Therefore, although He cannot make what is past not to have been past, taking "past" formally, He can nevertheless bring about the thing that has passed without its having passed. And thus He can make Adam not to have been.

2. To make this evident, it must be considered that, although something may have the character of an accident per accidens in relation to the nature of a thing considered absolutely, nothing prevents it from being related to that nature as existing under some posited condition so as to befit it per se: just as, although the gathering of sight is accidental with respect to Socrates considered absolutely, it is nevertheless related to him as existing under blackness, and thus, in this respect, is per se, because it enters into the account of blackness. So too, although a relation to this or that time befits a temporal thing considered absolutely only per accidens, because its account abstracts from every difference of time—for it lies outside the account of man that he be measured at this or that time, since the nature considered absolutely abstracts from every difference of time—nevertheless, if the nature is considered as existing in act temporally, it is necessarily measured by some difference of time; for it would not be a temporal thing unless its existence were measured by time. Therefore a thing, as having esse in act temporally, cannot be separated from a relation to time, since such a relation formally enters into the actual esse of the temporal thing, insofar as it is temporal. And just as a thing now actually existing, as such, is necessarily accompanied by a relation to present time, so that it cannot fail to exist during the present time in which it is—otherwise it would at once exist and not exist—even though God can make a thing now existing not exist in the following time, and could have made it not exist; so also a thing which was, say Adam, although God could absolutely have made it never exist, yet if it is posited to have had the esse of actual existence in some time, God cannot separate it from pastness, which names a relation to time past for us; just as, when it was in time present to us, insofar as it was such, He could not separate it from presentness, which is a relation to present time. Therefore Saint Thomas says well in the text that it is of the same necessity that something be while it is, and that something have been while it was.

3. To the objection it is said, therefore, that although pastness is an accident by accident with respect to Adam taken absolutely—and thus God could have made Adam not to have been, because He could have not produced Adam—nevertheless with respect to Adam as he was in past time it belongs to him not by accident but per se. Therefore Adam who was cannot be not to have been without contradiction, supposing that he once was. What is said to be impossible per accidens is so because it is impossible on account of a supervening accident, namely pastness: once this is posited, then what is posited is impossible per se, namely that the past not be past; just as it cannot come about that this black thing, supposing it to be black, not be seen by the congregative sense, nor can it come about that in this time in which it is black it not be black, because it would at once be black and not be black.

4. But if it is further pressed: since, although pastness belongs to Adam per se insofar as he is past, yet it belongs to Adam considered in himself only per accidens; therefore it can be separated from him — the reply is that, although anything per accidens can absolutely be separated from that to which it belongs per accidens, still it cannot be separated for that measure of time for which it is present: for then it would at once be and not be in reality. Therefore, since pastness in every time after that time in which it was true to say "Adam is" belongs to Adam himself — because pastness pertains to the ratio of that of which it was once true to say "this is," inasmuch as it is such — for it was once true that Socrates runs, which is, that Socrates has run — there is no time at which pastness can be separated from Adam, even though "Adam was not," with the rationes of the terms precisely considered, is possible.

Concerning those things that pertain to the divine knowledge and will, enough has been said in the First Book ². But concerning the other matters touched upon here, treatment is given in particular in various places of this Work. Therefore they are not to be treated in this place, but each in its own place.