Post-structuralist thought

Gilles Deleuze:
  [S]ubject and object are metaphysical categories; they presuppose
  the notions of unity and identity. They are categories of a
  'vertical' philosophy (like Hegel's). The singular aspect of all
  vertical philosophy is the separation in it of the truth of the
  concept from the reality to which it refers.

Jacques Derrida:
  'I try to place myself at a certain point at which ... the thing
  signified is no longer easily separable from the signifier.'

Michel Foucault:
  Madness here has its own form of reason and is seen as a general
  characteristic of human beings. Unreasonable reason, and reasonable
  unreason could exist side by side.
  [...] Discontinuity (between eras) thus predominates in the history
  of madness.
  [...] Knowledge is [...] linked to power, and the prison becomes a
  tool of knowledge.