An analysis of the nature of reflexivity--a relation which relates a thing to itself although it is regularly used to relate two different things--is followed by specific discussions of its place and functions in the writings of various philosophers. These discussions substantiate the following theses: reflexivity is a basic structure common to different phenomena; although traditionally unacknowledged, it is a useful and important concept in philosophy as well as in other disciplines; acknowledging its existence and understanding its structure deepens our (...) understanding of philosophical systems; since, like any other philosophical tool, reflexivity can be used either legitimately or illegitimately, nothing in it is inherently flawed; a structural analysis of different types of reflexivity and the relations between them can be presented; the history of its use is marked by a tendency towards its "normalization". These discussions are intended to raise awareness and generate future studies of this important but neglected philosophical structure. (shrink)