"The knowledge of our own being we have by intuition. The existence of a God reason clearly makes known to us, as has been shown. "The knowledge of the existence of any other thing we can have only by sensation: for there being no necessary connection of real existence with any idea a man hath in his memory, nor of any other existence but that of God, with the existence of any particular man; no particular man can know the existence of any other being, but only when by actual operating upon him it makes itself perceived by him. For the having the idea of anything in our mind no more proves the existence of that thing, than the picture of a man evidences his being in the world, or the visions of a dream make thereby a true history. "It is therefore the actual receiving of ideas from without, that gives us notice of the existence of other things, and makes us know that something doth exist at that time without us, which causes that idea in us, though perhaps we neither know nor consider how it does it: for it takes not from the certainty of our senses, and the ideas we receive by them, that we know not the manner wherein they are produced, _v. g._, whilst I write this I have, by the paper affecting my eyes, that idea produced in my mind which, whatever object causes, I call white; by which I know that that quality or accident (_i. e._, whose appearance before my eyes always causes that idea) doth really exist, and hath a being without me. And of this, the greatest assurance I can possibly have, and to which my faculties can attain, is the testimony of my eyes, which are the proper and sole judges of this thing, whose testimony I have reason to rely on as so certain, that I can no more doubt, whilst I write this, that I see white and black, and that something really exists that causes that sensation in me, than that I write or move my hand: which is a certainty as great as human nature is capable of, concerning the existence of anything but a man's self alone, and of God.