Sometimes the things people say or the ideas they express just don’t make sense. We’ve all encountered this, and often on some level (perhaps intuitively) we know that what’s being said is in some way an untruth. Seeing as philosophy (which means love of knowledge) often involves the search for truth, it makes sense to outline some basic rules to help us find what is true and steer clear of what is fallacious.
One of Aristotle’s most important contributions to philosophy was his development of formal logic, and the principles he outlined are still in use today. There are three basic laws from which the other rules of formal logic are derived.
1. The Law of Identity
The law of identity is quite simple: it states that an object is the same as itself, or A = A. Aristotle says:
Now “why a thing is itself” is a meaningless inquiry (for—to give meaning to the question ‘why’—the fact or the existence of the thing must already be evident—e.g., that the moon is eclipsed—but the fact that a thing is itself is the single reason and the single cause to be given in answer to all such questions as why the man is man, or the musician musical, unless one were to answer, ‘because each thing is inseparable from itself, and its being one just meant this.’ This, however, is common to all things and is a short and easy way with the question.) – Metaphysics, Book VII, Part 17
It is important to understand exactly what Aristotle was saying. Whenever we identify a thing we are creating a dichotomy between that thing and the rest of the universe (symbolically, let’s say A and not-A). The next two laws follow from the law of identity (and they are not separate laws per se, but rather affirmations of what is implicit in the law of identity).
2. The Law of Non-Contradiction
Following logically from the identification of object A and the creation of two subsets (that is A and not-A) that is implicit in the Law of Identity, it is impossible for A to be both A and not-A at the same time and in the same relationship.
e.g. Consider the statement “Socrates is mortal and immortal.” The Law of Non-Contradiction states that Socrates cannot be both mortal and immortal.
3. The Law of the Excluded Middle
Again, following logically from the two subsets created by the Law of Identity, it is impossible for the object to be neither A nor not-A.
e.g. Consider the statement “Socrates is mortal or not mortal.” According to the Law of the Excluded Middle the “middle position” that Socrates is neither mortal nor not-moral cannot be true.
So the next time someone says something silly like “the only absolute truth is that there is no absolute truth” remind them to stop contradicting themselves and start making sense!