The Problem of Self-Evidence
The Problem of Self-Evidence
The quotation presented above comes from a section in the Summa contra gentiles in which Thomas argues against the idea that the existence of God is self-evident to us.12 Aquinas’s notion of self-evidence and its relationship to our knowledge of God likely has its origin in Boethius. He makes a distinction between that which is self-evident in itself, on the one hand, and that which is self-evident to us, on the other.
In Summa theologica, Thomas asks “Whether the Existence of God is Self-Evident?”13 After listing objections, Thomas has this to say:
I answer that, A thing can be self-evident in either of two ways; on the one hand, self-evident in itself, though not to us; on the other, self-evident in itself, and to us. A proposition is self-evident because the predicate is included in the essence of the subject, as “Man is an animal,” for animal is contained in the essence of man. If, therefore the essence of the predicate and subject be known to all (per se nota), the proposition will be self-evident to all; as is clear with regard to the first principles of demonstration, the terms of which are common things that no one is ignorant of, such as being and non-being, whole and part, and such like. If, however, there are some to whom the essence of the predicate and subject is unknown, the proposition will be self-evident in itself, but not to those who do not know the meaning of the predicate and subject of the proposition. Therefore, it happens, as Boëthius says (Hebdom., the title of which is: “Whether all that is, is good”), “that there are some mental concepts self-evident only to the learned, as that incorporeal substances are not in space.” Therefore I say that this proposition, “God exists,” of itself is self-evident, for the predicate is the same as the subject; because God is His own existence as will be hereafter shown (Q. III., A. 4). Now because we do not know the essence of God, the proposition is not self-evident to us; but needs to be demonstrated by things that are more known to us, though less known in their nature—namely, by effects.14
There are a number of aspects to this discussion that influence Thomas’s response.
First, the distinction between that which is self-evident in itself (per se) and that which is self-evident to us is located in propositions. This is an extremely important point in understanding Thomas. He defines that which is self-evident by way of the relationship between a subject and a predicate in a given proposition. So, that which is self-evident per se is any proposition in which the predicate is, in some essential sense, contained in the subject, such as “Man is an animal,” to use Thomas’s example. The notion of “animal” does not exhaust that of “man,” but the former is necessarily included in the latter.
A proposition, however, can be self-evident per se and not to us (non est nobis per se nota). The predicate of a proposition may in some essential way be contained in the subject, making the proposition self-evident per se, yet if the terms of that proposition are not known to us, then it is not self-evident to us. So, says Thomas,
For it is simply self-evident that God is, because the selfsame thing which God is, is His existence. But since we are unable to conceive mentally the selfsame thing which is God, that thing remains unknown in regard to us.15
Thomas argues that God’s existence is not self-evident to us because we are not able to conceive of something in our minds to which the term “God” would apply.
Thomas also uses this occasion to refute Anselm’s so-called “ontological argument.”16 In that argument, Anselm maintains that one who has the concept of “God” in his mind automatically includes in and with that concept the idea of one “than which none greater can be conceived.” In other words, the content always included in the term “God,” according to Anselm, is one “than which none greater can be conceived.”
Thomas disagrees with Anselm. There have been those, says Thomas, who have the notion of God in mind, but who have also concluded that “this world is God.”17 Furthermore, Thomas argues that the concept of God in the mind does not necessarily guarantee that such a one exists in reality.
In response to other possible affirmations of God’s subjective self-evidence, Thomas says that since God’s essence cannot be known, we must come to know him through his effects. He also insists that our “natural” knowledge of God is not a knowledge of God per se. Instead,
Man desires Him naturally in so far as he naturally desires happiness, which is a likeness of the divine goodness. Hence it does not follow that God considered in Himself is naturally known to man, but that His likeness is. Wherefore man must needs come by reasoning to know God in the likenesses to Him which he discovers in God’s effects.18
The existence of God, then, can in no way be self-evident to us. This point will be important as we move forward. In Thomas’s epistemology, there is an unmistakable appeal to that which he considers to be general and common—the “natural”—which itself provides the foundation for anything else that we can or do know about God.