Commentaria in Summam contra Gentiles, Liber I

Finally, Saint Thomas, bringing his prologue to a close, declares from what has been said his intention with respect to the manner of proceeding ¹. He first observes that, since there is a twofold truth concerning divine things, this duality of truth is not to be taken from the side of God himself, but from the side of our knowledge.

For the understanding of this, it must be considered that, since truth resides in the intellect's being adequate to the thing through its act of understanding—that is, while it apprehends the thing as it is—two elements are included in this: one that is real, namely the act of understanding; and another that belongs to reason, especially in God, namely the relation of adequation to the thing understood. If we speak of truth with respect to the very act of understanding, then in God there is one simple truth; indeed, He Himself is truth most simple, because one most simple intelligence understands the esse of all things. But if we speak of truth with respect to the relation of reason itself, then it is not unfitting that there be many truths in God, according as He is adequate to the many things understood by Him. Yet because He understands these many things in one, namely in His own essence, therefore He is said absolutely to be one simple truth. Our intellect, however, knows different complexes by different acts of understanding. Therefore, according to the multitude of its acts of understanding—not only with respect to the relation, but also with respect to the foundation and the act of understanding—there are many truths in it. When, then, we say that a twofold truth of divine things has been handed down to us, this is not to be understood as though God Himself possesses a twofold knowledge and has handed it on to us; but rather because of those things which God, knowing them in Himself with one cognition, has revealed to us, we possess a twofold cognition and a twofold truth.

Second, we may expound it thus. For truth can be taken in two ways: either, I say, as it is in the thing known, or as it is in the intellect. Here Saint Thomas speaks of truth as it is in the thing known, not however as it is in the intellect. For enuntiabilia about the same thing can be multiplied in two ways: namely, either because there are diverse things in the thing itself from which diverse enuntiabilia are constituted, just as of a musical and white man is understood that he himself is musical and that he himself is white; or because the thing indeed is in itself most simple, lacking all diversity, but nevertheless, because the intellect cannot comprehend it, it forms diverse concepts of it, imperfect and unequal, from which it constitutes diverse true enuntiabilia. The sense of Saint Thomas, therefore, is that this twofold truth, or diversity of true enuntiabilia, is not to be taken on the part of God himself, as if, namely, there were in him diverse things from which the diversity of enuntiabilia might be taken; rather he himself is one and simple truth on the part of the thing, because all the predicates attributed to the divine essence are identical with one another and also with the subject; but it is on the part of our intellect, which understands God in diverse ways and with diverse concepts, knowing some things about him naturally, others indeed through revelation.

II. This having been premised, Saint Thomas goes on to say that, in order to make manifest a truth naturally known, we must proceed both by demonstrative arguments and by probable ones, gathered from the books of the philosophers as well as of the Saints. — From this it is clear that not all the arguments set down by the holy Doctor in this book are to be defended as demonstrative: since he himself says that he wishes to introduce some that are merely probable.

For the manifestation of truth known supernaturally, the aim ought not to be that the adversary be convinced by arguments, but rather that the arguments of the adversaries be resolved, and that the truth be shown forth from the authority of Scripture, confirmed by miracles. It will not, however, be useless to bring forward probable arguments for the exercise and consolation of the faithful, but not for convincing adversaries.