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

At the same time, how "I who think" is distinct from the "I" which intuites itself (other modes of intuition being cogitable as at least possible), and yet one and the same with this latter as the same subject; how, therefore, I am able to say; "I, as an intelligence and thinking subject, cognize myself as an object thought, so far as I am, moreover, given to myself in intuition--only, like other phenomena, not as I am in myself, and as considered by the understanding, but merely as I appear"--is a question that has in it neither more nor less difficulty than the question--"How can I be an object to myself?" or this--"How I can be an object of my own intuition and internal perceptions?" But that such must be the fact, if we admit that space is merely a pure form of the phenomena of external sense, can be clearly proved by the consideration that we cannot represent time, which is not an object of external intuition, in any other way than under the image of a line, which we draw in thought, a mode of representation without which we could not cognize the unity of its dimension, and also that we are necessitated to take our determination of periods of time, or of points of time, for all our internal perceptions from the changes which we perceive in outward things.