The law of non-contradiction

P v ¬P

By Spencer D Gear

“Aristotle was one of the first recorded ancient thinkers to discover the law of non-contradiction. It is important to note that Aristotle did not create this law, no more than Isaac Newton created the law of gravity; he merely discovered it as an unchanging principle of the universe” (Josh 2008).

In his writing, Metaphysics, famous Greek philosopher, Aristotle, wrote: “Such a principle is the most certain of all; which principle this is, let us proceed to say. It is, that the same attribute cannot at the same time belong and not belong to the same subject and in the same respect” (Aristotle n.d.).

This is known as the law of non-contradiction, which is one of the first principles of knowledge. “The law of non-contradiction can be expressed simply as such: A cannot be both B and non-B at the same time and in the same sense (Josh 2008).

Ravi Zacharias told of an instance when he was debating a professor who embraced the dialectical logic of the Hindu religion.

As the professor waxed eloquent and expounded on the law of non-contradiction, he eventually drew his conclusion:  “This [either/or logic] is a Western way of looking at reality.  The real problem is that you are seeing contradictions as a Westerner when you should be approaching it as an Easterner.  The both/and is the Eastern way of viewing reality.”

After he belabored these two ideas on either/or and both/and for some time, I finally asked if I could interrupt his unpunctuated train of thought and raise one question.

I said, “Sir, are you telling me that when I am studying Hinduism I either use the both/and system of logic or nothing else?”

There was pin-drop silence for what seemed an eternity.  I repeated my question:  “Are you telling me that when I am studying Hinduism I either use the both/and logic or nothing else?  Have I got that right?”

He threw his head back and said, “The either/or does seem to emerge, doesn’t it?”

“Indeed, it does emerge,” I said.  “And as a matter of fact, even in India we look both ways before we cross the street – it is either the bus or me, not both of us” (Zacharias 1994:129).


Aristotle n.d., Metaphysics (online), 4.3, transl. W. D. Ross, Available from: (Accessed 10 August 2008).

Josh 2008., “The nature of truth (Part 2): The principle of non-contradiction,” Quadrivium (online), 6 April, available from: (Accessed 10 August 2008).

Zacharias, R. 1994. Can Man Live Without God?, Dallas: Word Publishing.


Copyright © 2010 Spencer D. Gear. This document last updated at Date: 29 January 2018.