Aristotle’s Laws of Thought

Aristotle's "Laws of Thought" date back to the earliest days of Western Philosophy. They shape the basic structure of Western philosophy, science, and its overall worldview - the worldview that can so puzzle many non-Westerners. Many philosophers who followed Aristotle, such as Locke, Leibnitz and Schopenhauer, have modified and enhanced his principles. However, the initial intent has remained the same. These laws are fundamental logical rules, with a long tradition in the history of philosophy, which together define how a rational mind must think. To break any of the laws of thought (for example, to contradict oneself) is to be irrational by definition. These three classic laws of thought were fundamental to the development of classical logic. They are:

• Law of identity - an object is the same as itself: “A is A”


• Law of noncontradiction - contradictory statements cannot both at the same time be true, e.g. the two propositions "A is B" and "A is not B" are mutually exclusive.


• Law of excluded middle - Everything must either be or not be. There is no in-between.

These are self-evident logical principles - axioms that cannot be proved (or disproved), but must be accepted (or rejected) a priori. Other postulates could be substituted for them, and in fact have been in other traditions such as Buddhism, which celebrates contradiction. Even Greek philosophy before Aristotle (and Parmenides, who proposed similar laws) did not always embrace these concepts. But practically everything we know of traditional Western Philosophy and Logic embodies these principles. Preceding Aristotle by over a century, Heraclitus believed that contradictions were necessary - that their existence was essential to a thing's identity:

"Not only could it be stated that identity is the strife of oppositions but that there could be no identity without such strife within the entity."

He argued that because all things change, they must have already had in them "that which they were not". Only the existence of such contradictions could account for the change we see in the world. For example,

"Cold things grow warm; warm grows cold; wet grows dry; parched grows moist."

The defenders of Aristotle’s three laws of thought quickly learned that they had to establish the context for the application of these laws, because they were frequently assailed with counter-examples that seemed to violate them. It became clear that the laws could not be employed loosely or in poorly defined conditions. So, they began to require a “definite logic” model. In this model, the terms and the expressions formed from these terms must be clearly definable and knowable. But this ideal is rarely achieved in the real world, and we are forced to make assertions about things in less than precise, fuzzy terms. Not until the creation of Mathematical Logic by Boole in the 19th century, and later Russell and others, was logic able to refine its expression with mathematical, perfectly clear terms and operations.

This development in logic admirably suited the predispositions of the Western mind. Western philosophy to a very large extent has been founded upon the Laws of Thought and similar ground rules. We believe that our thinking should strive to eliminate ideas that are vague, contradictory, or ambiguous, and the best way to accomplish this, and thereby ground our thinking in clear and distinct ideas, is to strictly follow laws of thought.

In spite of how dominant these laws of thought have been, they have not been without their critics, and philosophers from Heraclitus to Hegel have leveled powerful arguments against them. But the issue does not seem to be whether the laws are applicable or not, but where and when are they applicable? Certainly, the laws of thought have a place, but what is that place? As Walt Whitman wrote in “Song of Myself”:

"Do I contradict myself?
Very well, then, I contradict myself.
(I am large, I contain multitudes.)"

Also as Nagarjuna, one of the fathers of Buddhism, wrote in "Verses on the Middle Way":

"Everything is real and not real.
Both real and not real.
Neither real nor not real.
That is Lord Buddha's teaching."

The time to abandon strict laws of thought arises when we are beyond the realm to which ordinary logic applies, or as when “the sphere of thought has ceased, the nameable ceases.” A similar sentiment is expressed by Wittgenstein's assertion in the Tractatus,

"what can be said at all can be said clearly, and what we cannot talk about we must pass over in silence"

It would be very narrow minded, indeed, as well as barren and joyless, to try to apply these or similar laws to every human experience. However, in the narrow, modest realm of science, whose goal is merely to explain how things work and of what they are made, this type of restricted and disciplined thought is a perfect fit.