 By the time of the second edition of the Critique, however, Kant must have come to see the need for a positive defense of the assumption of the existence of things in themselves that ground our spatio-temporal representations of body (although, since those things in themselves are not supposed to be spatio-temporal and causality is supposed to be a spatio-temporal relation, they cannot precisely be said to cause our spatio-temporal representations). Kant’s argument—which in the following years he would attempt to improve a dozen times (see Guyer 1983, Guyer 1987: Part IV, and Kant 2005)—is that we can only achieve “empirically determined consciousness” of our own existence, or a determinate temporal ordering of our own representations, by correlating them with something enduring outside of and distinct from them: