“Philosophy” refers to any inquiry that proceeds using reason. In other words, any attempt to understand the truth of any topic using reason is a philosophical inquiry. As I argue later in this book, there is no evidence for the existence of any metaphysical or objective fact or law that requires the adoption of any particular moral values. This means that there is no evidence for any metaphysical or objective fact or law that requires one to value truth or the pursuit of truth.

However, while there are no grounds for believing that anyone has an obligation to value truth or the pursuit of truth, it is not possible to engage in philosophy without valuing both. The most effective philosophers are those who are willing to pursue truth as disinterestedly as possible and accept any conclusions that are required by the evidence, regardless of the consequences—that is, regardless of how those conclusions make them feel or whether they reflect what they want to be true. But this is not an easy thing to do. 

“Reason” refers to the faculty of the mind that weighs alternative explanations based on their perceived correspondence to experience and their perceived accordance with the rules of logic. It is impossible to reason without thinking and it is impossible for humans to express thoughts except through language. Thus, philosophy, which consists of expressed thoughts based on reason, is not possible except through language.

There are three laws of thought, which Aristotle originally identified: (1) the law of identity, (2) the law of noncontradiction, and (3) the law of the excluded middle.

Under the law of identity, a thing is itself: “A is A.” This is a law of consistency in meaning across time within a given discourse. A concept must be used consistently within a discourse in order for that discourse to have any kind of internal coherence. Whether a discourse corresponds to experienced reality is a separate question, but it is impossible to rationally engage rationally in an internally inconsistent discourse.

Under the law of noncontradiction, a thing cannot be both itself and its opposite: “Not both A and not-A.” A spoon cannot not be a spoon and a mountain cannot not be a mountain. This is not to say it is not possible to debate the height a particular segment of land must be in order for it to be considered a mountain or how round and deep the large end of a utensil must be in order for it to be considered a spoon, only that once one has a clear idea of what such words refer to, it is not possible to coherently assert that these words refer to non-spoons and non-mountains.

Under the law of the excluded middle, a thing must either have a given attribute or not have that attribute: “Either A or not-A.” More specifically, a thing cannot have one attribute and a contradictory attribute at the same time and in the same manner. A spoon must either be round on the end or not round on the end. However, part of a spoon can be round while another part is not round, meaning it is possible to assert that a spoon is both round and not-round, but not in the same manner. Similarly, a mountain can become higher or lower across millions of years, so that the same mountain can have a height above 2,800 meters in elevation at one time, such as Mount Saint Helens before May 18, 1980, and below 2,800 meters at another, such as Mount Saint Helens today. Thus, the same mountain can be said to have a height both above 2,800 meters and below 2,800 meters, but not at the same time.

Despite their name, the three laws of thought formulated by Aristotle really describe the limits of what can be coherently expressed in language, not necessarily the limits of what exists. While not all experiences or mental events occur in terms of language, all thoughts occur in terms of language. Thus, the laws of thought formulated by Aristotle also describe the limits of what can be coherently thought.

But these laws do not necessarily describe the limits of what exists. It is possible that some aspects of existence are ineffable—that is, not possible to describe using language. But because they are outside the scope of language, these aspects of existence—if, indeed, they exist—are also outside the scope of thought, therefore outside the scope of reason, and therefore outside the scope of philosophy. Put another way, any statement that violates the laws of thought must be untrue, outside the scope of human thought, or both.