Peirce is clearly Americaś candidate for a place on the roster of the great philosophers. The issues in the philosophy of science, epistemology and the philosophy of mind that were central to his philosophical project just happen to be ones that are still on the center stage on the contemporary philosophical scene. Peirce nowhere gives us a unified official exposition of his own theory of knowledge. We can ilustrate his opinions by the examination of three fundamental forms of inference: deduction, induction and abduction. Demonstration of these kinds of inference is one of the ways how to explain Peirceś theory of scientific inquiry.