L'Être et le Néant
Subjectivity was rejected by Foucault and Derrida in favor of constructionism, but Satre embraced and continued Descartes' work in the subject by emphasizing subjectivity in phenomenology. Sartre believed that, even within the material force of human society, the ego was an essentially transcendent being -- posited, for instance, in his opus "Being and Nothingness" through his arguments about the 'being-for-others' and the 'for-itself' (i.e., an objective and subjective human being).