The Prince of Principles

by Andrew Nimmo

There is nothing more practical than a theory. All actions are based on ideas. It is very important, therefore, that one's ideas be conformed to objective reality and sound principles.

Principles are the beginnings of things and of thought. Because principles are “firsts” and are required for reasoning and proof, they themselves cannot be proven, they are beyond proof - so clearly evident that proof is neither possible nor required. If principles required proof there would have to be other principles to lead to them (which required no proof) and so on ad infinitum. If everything has to be proven there can be no knowledge. But we have knowledge. Therefore, not everything, such as principles, requires proof. Even though principles cannot be proven they can be defended. One way of defending them is by demonstrating the contradiction that follows by denying them.

The Supreme Principle

The Supreme Principle is the principle upon which all reality and all thought are based and which every other principle presupposes. It is not possible to contradict the Supreme Principle in fact, and to attempt to do so in thought is to make the very act of thought impossible. A brief inspection of the ways in which the principle is expressed makes this evident:


The Supreme
Principle may
be expressed as:
{ 1. The Principle of Identity: A is A
2. The Principle of non-Contradiction: A is not non-A
3. The Principle of the Excluded Middle: Between A and non-A there is nothing.

1. The Principle of Identity

A is A. The Principle of Identity simply affirms that a thing is what it is, is one with itself. A tree is a tree. A man is a man. Every act of every man accords with this principle. It is self-evident.

2. The Principle of Non-Contradiction

A is not non-A. This principle denies that a thing is its own opposite. A tree is not a non-tree. This means that while a tree is a tree it cannot be anything else. By having the nature of tree it excludes everything else, i.e. what is non-tree. We can divide the universe according to this principle. The universe is divided into John Smith and everything else that is not John Smith, or into beings endowed with reason and beings without reason, or into beings with life and beings without life. To assert that a thing is both what it is and not what it is is clearly absurd. Non-contradiction is the essential precondition for a thing to exist or to be makeable.

3. The Principle of the Excluded Middle

Between A and non-A there is no middle. This principle states that there is no middle ground between something and its contradictory opposite. It has many applications. For example, a thing is either a tree or it is not. If it si not a tree then it is something else. But there is no middle term between be and be-not, between yes and no. If we cancel out tree and non-tree, which, in contradictory opposition, is everything other than tree, there is nothing left. Similarly, in psychology we see that a thing is either living or non-living. There is nothing in between. A living thing is either a knower or a non-knower. This is the dividing line between plants which have no knowledge and things higher than plants. If a thing appears at first to be a plant but exhibits definite signs of sense knowledge it is an animal. There is no third thing between plant and animal because there is no middle between knower and non-knower, between be and be-not. This can be applied also to the distinction between rational animal (man) and irrational animal, and between Creator and creature.

To deny the Supreme Principle is to affirm it; otherwise the very word “deny” could mean its own opposite, i.e. “affirm”. In order to deny anything one must accept that “deny” means “deny”, “is one with itself”, thereby affirming the principle of identity, an expression of the Supreme Principle.

Andrew Nimmo


Andrew Nimmo is a lecturer at the Centre for Thomistic Studies, in Sydney, Australia.

This article posted December 1997. It was published in Universitas, Vol 1 (1997), No. 2.
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