Click on the phrases to see them in context. The original texts by Immanuel Kant and David Hume are available from the Gutenberg Projet.

Now as we cannot cognize completely a priori the existence of any object of sense, though we can do so comparatively a priori, that is, relatively to some other previously given existence--a cognition, however, which can only be of such an existence as must be contained in the complex of experience, of which the previously given perception is a part--the necessity of existence can never be cognized from conceptions, but always, on the contrary, from its connection with that which is an object of perception.