Scholasticism … is only popular philosophy made systematic—William James.

The principle of existence relies on the three foundational principles of logic, epistemology, and metaphysics: the principle of identity, the principle of noncontradiction, and the principle of excluded middle. These principles are the most basic properties of reality and form the foundation of what we can know about the world and how to correctly think about it. Many of us use these principles day in and day out without ever really thinking about them. These principles, like the principle of existence, are undeniable because one must use these principles in any attempt to deny them.

Everyone uses the principle of noncontradiction one way or another. Whenever we change the oil in our automobiles, drive to work, or simply try to write or speak a conceptually coherent sentence, we are using the principle of noncontradiction.

In our last post, we explored the principle of existence and why it is such an important principle in cosmological reasoning. This time we will discover how the principle of noncontradiction relates to our cosmological argument from being.

The principle of noncontradiction is this: nothing can both be and not be at the same time and same relationship. Another way of putting the principle is this: A cannot be both B and non-B at the same time and in the same relationship. We understand this principle intuitively. I cannot both exist and not exist at the same time (this is a statement of being, or existence). Further, I can be both a father and son at the same time but not in the same relationship (this is a statement of the being, or existence, of relationships).

Aristotle was among the first to articulate the principle of noncontradiction. He reminds us,

There is a principle in things about which we cannot be deceived, but must always, on the contrary recognize the truth,—viz. that the same thing cannot at one and the same time be and not be, or admit any other similar pair of opposites.¹

And,

By the starting-points of demonstration I mean the common beliefs, on which all men base their proofs; e.g. that everything must be either affirmed or denied, and that a thing cannot at the same time be and not be, and all other such premises.²

Why is the principle of noncontradiction important in cosmological reasoning for the existence of God? So far we have seen that the principles of existence and identity cannot be legitimately doubted. The same is true for the principle of noncontradiction. One must assume the principle when trying to deny it. As we shall see, the three main principles of epistemology, metaphysics, and logic are all based on the properties of being. Being is undeniable. Being itself provides the foundation of rational thought and discussion about it. In grounding our theistic argument in being, therefore, we are simply explaining why it is impossible to deny reality. We are faced with only two propositions: either being or non-being (nothing). In the realm of being, we will come to understand the realm of becoming or change—but the argument is based on being, not becoming.

I will explicate this a little more in our next post about the principle of excluded middle. For now, it is important to see how the argument itself reflects the metaphysical principles of reality or being. As Thomas Aquinas would remind us, being is the proper effect of God.

Here is the introduction to this series

Here is the first part.

Here is the second part.

Here is the third part.

1 Aristotle, Metaphysics, trans. W. D. Ross, vol. 7, Great Books of the Western World (Chicago: Encyclopedia Britannica, Inc., 1996), 590.

2 Aristotle, Metaphysics, trans. W. D. Ross, vol. 7, Great Books of the Western World (Chicago: Encyclopedia Britannica, Inc., 1996), 515.