The conclusion of Descartes's cogito is an ontological certainty, 'I may be deceived about everything else but not my own existence'. There is also an epistemological version of this: I might have no autonomy, and be only a simulation of agency, but the fact that this simulation requires my belief in my freedom-to-discover-the-truth-of-my-situation means that this belief is an essential component of the simulation. What constitutes this belief is that it is about my true situation, so even if it is incorrect it is in an irreducible relation to my true situation nevertheless and retains the possibility of being correct. This argument is analogous to asking of someone who asserts that consciousness is an illusion, 'whose illusion?'