concept

käsite, konsepti abstract and general idea; an abstraction
understanding retained in the mind, from experience, reasoning and/or imagination; a generalization (generic, basic form), or abstraction (mental impression), of a particular set of instances or occurrences (specific, though different, recorded manifestations of the concept).
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Frege's concepts are very nearly propositional functions in the modern sense. Frege explicitly recognizes them as functions. Like Peirce's rhema, a concept is unsaturated. They are in some sense incomplete. Although Frege never gets beyond the metaphorical in his description of the incompleteness of concepts and other functions, one thing is clear: the distinction between objects and functions is the main division in his metaphysics. There is something special about functions that makes them very different from objects.