I understand by idea a necessary conception of reason, to which no corresponding object can be discovered in the world of sense.
Accordingly, the pure conceptions of reason at present under consideration are transcendental ideas.They are conceptions of pure reason, for they regard all empirical cognition as determined by means of an absolute totality of conditions.They are not mere fictions, but natural and necessary products of reason, and have hence a necessary relation to the whole sphere of the exercise of the understanding.