We, humans, couldn't have abstracted the identity of indiscernibles and self-identity from our sense perception; the existence of space precludes the possibility of two objects (a,b) being identical--no two objects can possibly occupy the same space. On the other hand, the existence of time precludes the possibility of a single object (a) being identical with itself-- no object can maintain the same properties (mass, volume, color, the coordinates of its electrons orbiting the nuclei .etc...) over time. Still, we hold that a=a and a=b ,with certainty.
Where do we get this apparently a priori knowledge of identity then, if not from experience?