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

Speculative reason has thus, at least, made room for such an extension of our knowledge; and, if it must leave this space vacant, still it does not rob us of the liberty to fill it up, if we can, by means of practical data--nay, it even challenges us to make the attempt.*