I agree with reggin's post. You definitely need to look at Hume's problem of induction. Then look at Kant's claim that there is such a thing as synthetic, a priori truths. You can then look at how Hume would reply. I haven't read Sartre, but I know Bertrand Russell criticized Kant's argument in his Problems of Philosophy.
If I knew how you were structuring the paper, I could give you more advice. If you are including Plato, you might also want to look at Aristotle response to him concerning universals and particulars. Also, for Kuhn, his paradigm shifts is important, but the main thing you want to look at for this topic is his claim that all observations are dependent on background knowledge (generally referred to as observations being theory dependent).
