The Origin of Knowledge
  On one view the only origin of our knowledge is experience (this is the "empiricist" position - the word comes from the Greek meaning experience). 
Here is how Locke put it:

Let us then suppose the Mind to be, as we say, white Paper, void of all Characters, without any Ideas; How comes it to be furnished? Whence comes it by that vast store, which the busy and boundless Fancy of Man has painted on it, with an almost endless variety? Whence has it all the materials of Reason and Knowledge? To this I answer, in one word, From Experience: In that, all our Knowledge is founded; and from that it ultimately derives it self. (John Locke, An Essay concerning Human Understanding, fourth edition, originally published in London, 1700, bk. II, ch. I, §2).

Others claim that we know some things independently of experience. Kant, for instance, wrote:

It is easy to show that there actually are in human knowledge judgments which are necessary and in the strictest sense universal, and which are therefore pure a priori judgements. If an example from the sciences be desired, we have only to look to any of the propositions of mathematics ..." (Immanuel Kant, Critique of Pure Reason, originally published in Riga, 1781, Introduction, §II).