In philosophy, an aporia is a conundrum or state of puzzlement. In rhetoric, it is a declaration of doubt, made for rhetorical purpose and often feigned. The notion of an aporia is principally found in ancient Greek philosophy, but it also plays a role in modern post-structuralist philosophy, as in the writings of Jacques Derrida and Luce Irigaray, and it has also served as an instrument of investigation in analytic philosophy.