From this process of generalization, or synthesis, we create from our simple concepts our _general concepts_. Some of the older authorities distinguished between these two classes by terming the former "conceptions," and reserving the term "concepts" for the general concepts. Brooks says of this: "The products of generalization are general ideas called _concepts_. We have already discussed the method of forming conceptions and now consider the nature of the concept itself.... A concept is a general idea. It is a general notion which has in it all that is common to its own class. It is a general scheme which embraces all the individuals of the class while it resembles in all respects none of its class. Thus my conception of a _quadruped_ has in it all four-footed animals, but it does not correspond in all respects to any particular animals; my conception of a _triangle_ embraces all triangles, but does not agree in details with any particular triangle. The general conception cannot be made to fit exactly any particular object, but it teems with many particulars. These points may be illustrated with the concepts _horse_, _bird_, _color_, _animal_, etc." So we may begin to perceive the distinction and difference between a _concept_ and a _mental image_. This distinction, and the fact that _a concept cannot be imaged_, is generally difficult for the beginner. It is important that one should have a clear and distinct understanding regarding this point, and so we shall consider it further in the following chapter. CHAPTER V. CONCEPTS AND IMAGES As we have said, a concept cannot be imaged--cannot be used as the subject of a mental image. This statement is perplexing to the student who has been accustomed to the idea that every conception of the mind is capable of being reproduced in the form of a mental image. But the apparently paradoxical statement is seen as quite simple when a little consideration is given to it. For instance, you have a distinct general concept of _animal_. You know what you mean when you say or think, _animal_. You recognize an animal when you see one and you understand what is meant when another uses the word in conversation. But you cannot form a mental image of the concept, _animal_. Why? Because any mental image you might form would be either a picture of _some particular animal_ or else a composite of the qualities of several animals. Your concept is too broad and general to allow of a composite picture of _all animals_. And, in truth, your concept is _not a picture of anything that actually exists_ in one particular, but an abstract idea embracing the qualities of all animals. It is like the algebraic _x_--a symbol for something that exists, but not the thing itself.