qualities retained as the measure by which to test the admission of other
individuals into this class. The process of classification is made possible by what
the psychologist calls the concept. The concept enables us to think birds as well
as bluebirds, robins, and wrens; it enables us to think men as well as Tom, Dick,
and Harry. In other words, the concept lies at the bottom of all thinking which
rises above the seeing of the simplest relations between immediately present
objects.
Growth of a Concept.—We can perhaps best understand the nature of the
concept if we watch its growth in the thinking of a child. Let us see how the
child forms the concept dog, under which he is able finally to class the several
hundred or the several thousand different dogs with which his thinking requires
him to deal. The child's first acquaintance with a dog is, let us suppose, with a
pet poodle, white in color, and named Gyp. At this stage in the child's
experience, dog and Gyp are entirely synonymous, including Gyp's color, size,
and all other qualities which the child has discovered. But now let him see
another pet poodle which is like Gyp except that it is black in color. Here comes
the first cleavage between Gyp and dog as synonyms: dog no longer means
white, but may mean black. Next let the child see a brown spaniel. Not only will
white and black now no longer answer to dog, but the roly-poly poodle form also
has been lost; for the spaniel is more slender. Let the child go on from this until
he has seen many different dogs of all varieties: poodles, bulldogs, setters,
shepherds, cockers, and a host of others. What has happened to his dog, which at
the beginning meant the one particular little individual with which he played?
Dog is no longer white or black or brown or gray: color is not an essential
quality, so it has dropped out; size is no longer essential except within very
broad limits; shagginess or smoothness of coat is a very inconstant quality, so
this is dropped; form varies so much from the fat pug to the slender hound that it
is discarded, except within broad limits; good nature, playfulness, friendliness,
and a dozen other qualities are likewise found not to belong in common to all
dogs, and so have had to go; and all that is left to his dog is four-footedness, and
a certain general form, and a few other dog qualities of habit of life and
disposition. As the term dog has been gaining in extent, that is, as more
individuals have been observed and classed under it, it has correspondingly been
losing in content, or it has been losing in the specific qualities which belong to it.
Yet it must not be thought that the process is altogether one of elimination; for
new qualities which are present in all the individuals of a class, but at first
overlooked, are continually being discovered as experience grows, and built into