Forgive me for my long-windedness on this one. If you like to think about things you may think it is worth reading this, but if you prefer to read the Paw-litics board passively, you may want to skip right over this thread. For those that do not know much about philosophy this discussion centers around the branch of philosophy commonly known as "epistemology."
Generally, epistemology is the "science" that studies the nature and means of human knowledge. I started out writing this thing myself and then discovered that other people have already put the effort into explaining various portions of this so I have copied and pasted much of other people's explanation in the interest of efficiency. We have actually skipped right over the step of metaphysics to discuss the current topic - I intend to get to metaphysics soon so everyone will see how everything can work together. Although Randerizer has pointed out this is something out of order - good epistemology is based on good metaphysics, I think there is still some value to discussing the topics in the order they have been addressed.
Short answer to the title of the thread: All knowledge fundamentally comes from sensory perception. Knowledge cannot be intrinsic.
PROOF
Roadmap: the proof relies on two central points (1) knowledge is knowledge of reality, and (2) existence has primacy over consciousness. These two points are irrefutable, as set forth below, because epistemology would otherwise be impossible. Regarding the second point - if thought created reality, no science offering guidance to thought would be applicable; consciousness could assert whatever it wished, and reality would have to obey. Regarding the first point - human knowledge, although based on sensory perception, is conceptual in nature. Human knowledge is not automatic or infallible; it can err, distort, or depart from reality. It can do this through ignorance or evasion. Humans therefore have to learn how to use their minds to distinguish truths from falsehoods.
More to come...