Andrew Bowie in AIA News:
In Sincerity and Authenticity (1972) liberal critic Lionel Trilling distinguished between two particular ways of being in the modern world. Being ‘sincere’ (from Latin sincerus, of things, ‘whole, clean, pure, uninjured, unmixed’), ‘true to oneself’ by not ‘dissembling’, becomes an ideal during the early emergence of bourgeois individualism. Its new significance coincides with the increase in social mobility, mobility which also offered more chances for pretending to be what one wasn’t. Shakespeare’s plays often deal with this issue. However, being true to oneself by not pretending to be other than one’s social role dictates subsequently often comes to be seen as merely a kind of conformism that precisely lacks ‘authenticity’. This demands doing things on one’s own authority, which can be seen in terms of being ‘author of oneself’. Diderot’s Rameau’s Nephew (1761), a dialogue with an eccentric man who is able to play character roles at will but who cannot stably adhere to any role for himself, explores the problems associated with self-authorship, and Hegel quotes the text in the Phenomenology of Spirit when explicating modern forms of consciousness.
Authenticity, then, demands truth to oneself of a different order from sincerity. Trilling dramatises this by reference to Joseph Conrad’s Heart of Darkness, where the atrocities committed by Kurtz (which are based on the genocide committed by the Belgians in the Congo in the 19th century) are seen as linked to his plumbing the depths of what he is capable of: being ‘true to oneself’ here leads to sheer horror.
More here.