ABSTRACTION (Let. abs, away + trahere, to draw). In logic, the process by which the mind separates out marks or characteristics which are similar in various objects, and disre gards the marks or characteristics by which the objects differ. It also °emirs where characteris ties of particular objects, or classes of objects, are replaced by a more general characteristic. An instance of the first kind is the formation of the class "biped" by the inclusion of all two legged animals. An instance of the second type is the substitution of the general mark "repro duction" for the more special marks, "vivipa rous," "oviparous," "fissiparous," etc. The re sult of this process is also called an abstraction, or, if it appears as a word, a concept. The psy chology of abstraction consists in describing the way in which the attention, in passing from one object to another, fastens upon an element com mon to all and dissociates it from its context.
Abstraction is carried out in a state of active attention (see ATTENTION), as when the phi lologist searches out common or allied roots in different languages. or when the geologist iden tifies strata in different localities and forms the abstraction of a single epoch in which they were laid. The process is, however, facilitated by the sheer decay of mental complexes; a decay which obliterates small differences and reduces mere similarity to indistinguishableness. It thus comes about that we form sketchy, "ab stract" images—as of "pen," "house," or "book" —from similar things, and that one of these schematic images is sufficient to call up a large number of more concrete tunobliterated) ideas whenever an appropriate incentive is given. (See AssocIATfox OF IDEAS.) Consult: R. 11. Lotze, Logic ittxford, 185s) ; W. dames, Prinei pits of Psychology (New York, ISHH).