A Concept, then, is seen to be a _general idea_. It is a general thought that embraces _all the individuals_ of its own class and has in it all that is common to its own class, while it resembles _no_ particular individual of its class in _all_ respects. Thus, a concept of _animal_ contains within itself the minor concepts of _all animals_ and the animal-quality of all animals--yet it differs from the _percept_ of any one particular animal and the minor concepts of minor classes of animals. Consequently a concept or general idea cannot be _imaged_ or mentally pictured. We may picture a percept of any particular thing, but we cannot picture a general idea or concept because the latter does not partake of the _particular_ qualities of any of its class, but embraces all the general qualities of the class. Try to picture the general idea, or concept, of Man. You will find that any attempt to do so will result in the production of merely _a man_--some particular man. If you give the picture dark hair, it will fail to include the light-haired men; if you give it white skin, it will slight the darker-skinned races. If you picture a stout man, the thin ones are neglected. And so on in every feature. It is impossible to form a correct general class picture unless we include every individual in it. The best we can do is to form a sort of _composite_ image, which at the best is in the nature of a symbol representative of the class--an ideal image to make easier the _idea_ of the general class or term. From the above we may see the fundamental differences between a Percept and a Concept. The Percept is the mental image of a real object--a particular thing. The Concept is merely a _general idea_, or general notion, of the common attributes of a class of objects or things. A Percept arises directly from sense-impressions, while a Concept is, in a sense, a pure thought--an abstract thing--a mental creation--an ideal. A Concrete Concept is a concept embodying the common qualities of a class of objects, as for instance, the concrete concept of _lion_, in which the general class qualities of all lions are embodied. An Abstract Concept is a concept embodying merely some one quality generally diffused, as for instance, the quality of _fierceness_ in the general class of lions. _Rose_ is a concrete concept; _red_, or _redness_, is an abstract concept. It will aid you in remembering this distinction to memorize Jevons' rule: "_A Concrete Term is the name of a Thing_; _an Abstract Term is the name of a Quality of a Thing_." A Concrete Concept, including all the particular individuals of a class, must also contain all the common qualities of those individuals. Thus, such a concept is composed of the ideas of the particular individuals and of their common qualities, in combination and union. From this arises the distinctive terms known as the _content_, _extension_ and _intension_ of concepts, respectively.