Imagination determines the limits of reality by way of possible objects and their counterfactual relations and causality, but it does not determine the limits of consciousness. It is much easier to imagine strange new worlds obeying different rules, even of time and space, than to imagine let alone describe a different consciousness. This is true even after you have experienced a range of different states. There could not be a Kantian style of deduction of consciousness, to know its limits and invariant properties, it cannot be 'got hold of' in that way. It is easier for some to doubt its existence altogether. Another axiom: consciousness is not susceptible of proof.