Now reason is the faculty of concepts. This may not, at first sight, be obvious. Reason, it might be objected, is the faculty of arguing, of drawing conclusions from premises. But a little consideration will show us that, though this is so, yet all reasoning is employed upon concepts. All reasoning is either deductive or inductive. Induction consists in the formulation of general principles from particular cases. A general principle is always a statement made, not about a particular thing, but about a whole class of things, that is, about a concept. Concepts are formed inductively by comparing numerous examples of a class. Deductive reasoning is always the opposite process of applying general principles to particular cases. If we argue that Socrates must be mortal because all men are so, the question is whether Socrates is a man, that is to say, whether the concept, man, is properly applied to the particular object called Socrates. Thus inductive reasoning is concerned with the formation of concepts, deductive reasoning with the application of them. Socrates, in placing all knowledge in concepts, was thus making reason the organ of knowledge. This was in direct opposition to the principle of the Sophists, who placed all knowledge in sense-perception. Now since reason is the universal element in man, it follows that Socrates, in identifying knowledge with concepts, was restoring the belief in an objective truth, valid for all men, and binding upon all men, and was destroying the Sophistic teaching that the truth is whatever each {145} individual chooses to think it is. We shall see this more clearly if we reflect that a concept is the same thing as a definition. If we wish to define any word, for example, the word man, we must include in our definition only the qualities which all men have in common. We cannot, for example, define man as a white-skinned animal, because all men are not white-skinned. Similarly we cannot include "English-speaking" in our definition, because, though some men speak English, others do not. But we might include such a quality as "two-legged," because "two-legged" is a quality common to all human beings, except mere aberrations and distortions of the normal type. Thus a definition is formed in the same way as a concept, namely, by including the common qualities of a class of objects, and excluding the qualities in which the members of the class differ. A definition, in fact, is merely the expression of a concept in words. Now by the process of fixing definitions we obtain objective standards of truth. If, for example, we fix the definition of a triangle, then we can compare any geometrical figure with it, and say whether it is a triangle or not. It is no longer open to anyone to declare that whatever he chooses to call a triangle is a triangle. Similarly, if we fix upon a definition of the word man, we can then compare any object with that definition, and say whether it is a man or not. Again, if we