It can also denote a process applied by linguists themselves, whereby phenomena are considered without the details that are not relevant to the desired level of analysis.
An early example of this kind of study came from John Horne Tooke, who in his conversational The Diversions of Purley (1786), proposed that the abstract word through came to English through both sound change and derivation from the Gothic: Tooke was incorrect about "through," but his insights about the way words migrated via geography, language, sound change, and meaning were innovative, and fundamentally correct.
For instance, Rudolf Carnap in his Introduction to Semantics (1942, Harvard University Press) writes: If… explicit reference is made to the speaker, or, to put it in more general terms, to the user of a language, then we assign it to the field of pragmatics.
(p. 9)A related statement was made a few years earlier by Carnap's fellow American philosopher Charles W. Morris, PhD student of the sociologist and pragmatist philosopher George Herbert Mead, and heavily influenced by the pragmatist and founder of (analytical) semiotics, Charles Sanders Peirce: "Syntactics, as the study of the syntactical relations of signs to one another in abstraction from the relations of signs to objects [i.e., semantics] or to interpreters [i.e., pragmatics], is the best developed of all the branches of semiotic."
Other analogous kinds of abstractions (sometimes called "emic units") include morphemes, graphemes and lexemes.