Or, in the same way, the family group may be enlarged until it takes in all the white people in a county, then all the white people in the state, then all in the United States; then all the white races, then all the white and other light-skinned races, then all mankind. Then, if one is inclined, the process may be continued until it embraces every living creature from moneron to man. Reversing the process, living creatures may be divided and subdivided until all mankind is seen to stand as a class. Then the race of man may be divided into sub-races according to color; then the white race may be subdivided into Americans and non-Americans. Then the Americans may be divided into inhabitants of the several states, or into Indianans and non-Indianans; then into the inhabitants of the several counties of Indiana, and thus the Posey Countians are reached. Then the Posey County people are divided into Smiths and non-Smiths; then the Smith family into its constituent family groups, and then into the smaller families, and so on, until the classification reaches one particular John Smith, who at last is found to be an individual--in a class by himself. This is the story of the ascending and descending processes of generalization. CHAPTER XXII. Classes of Concepts. In the preceding chapter we have seen the process of conception--of the forming of concepts. _The idea of a general class of things or qualities is a concept._ Each concept contains the qualities which are _common to all_ the individuals composing the class, but not those qualities which pertain only to the minor classes or the individuals. For instance, the concept of "bird" will necessarily include the common qualities of warm-bloodedness, featheredness, wingedness, oviparousness, and vertebratedness. But it will _not_ include color, special shape, size, or special features or characteristics of the subfamilies or individuals composing the great class. The class comprises the individuals and subclasses composing it; the concept includes the general and common qualities which _all_ in the class possess. A _percept_ is the mental image of a particular thing; a _concept_ is the mental idea of the general qualities of a class of things. A percept arises from the perception of a sensation; a concept is a purely mental, abstract creation, whose only existence is in the world of ideas and which has no corresponding individual object in the world of sense. There are two general classes of concepts, namely: (1) concrete concepts, in which the common qualities of a class of things are combined into one conceptual idea, such as "bird," of which we have spoken; (2) abstract concepts, in which is combined the idea of some _quality_ common to a number of things, such as "sweetness" or "redness." Jevons's well-known rule for terms is an aid in remembering this classification: "_A concrete term is the name of a thing; an abstract term is the name of a quality of a thing._"