Philosophical Lag - Philosophy lags behind the physical sciences. This notion is not original to Althusser but is advanced first by Gaston Bachelard. Althusser makes use of it in the essay Lenin and Philosophy.

Ideological State Apparatuses

Epistemological Break

Was Louis Althusser a Marxist?

Althusser was deeply concerned in both intellectual, political and perhaps personal ways with the question of what it meant to be a Marxist in philosophy.