καλέω, to call, a multitude called
"A class consists of several things coming under a common description"
(Whately, Logic, bk. I. sec. 3).
"The sorting of a multitude of things into parcels, for the sake of knowing
them better, and remembering them more easily, is classification " (Taylor,
Elements of Thought).
"Classification is a contrivance for the best possible ordering of the ideas of
objects in our minds; for causing the ideas to accompany or succeed one another
in such a way as shall give us the greatest command over our knowledge already
acquired, and lead more directly to the acquisition of more" (J. S. Mill Logic,
bk. IV. ch. 7).
"Abstraction, generalisation, and definition precede classification; for if we
wish to reduce to regularity the observations, we have made, we must compare
them, in order to unite them by their essential resemblances, and express their
essence with all possible precision.
"In every act of classification two steps must be taken; certain marks are to
be selected, the possession of which is to be the title to admission into the
class, and then all the objects that possess them are to be ascertained. When
the marks selected are really important and connected closely with the nature
and functions of the thing, the classification is said to be natural; where they
are such as do not affect the nature of the objects materially, and belong in
common to things the most different in their main properties, it is artificial"
(Thomson, Outline of Laws of Thought, 2nd ed., p. 377; 3rd ed., p. 343).
Classification proceeds upon observed resemblances. Generalisation rests upon
the principle, that the same or similar causes will produce similar effects
(Mill, Logic, bk. I. ch. VII. sec. 4; M'Cosh, Typical Forms, bk.
III. ch. I.).