Critical rationalism is the philosophy of Karl Raimund Popper. Critical rationalists hold the belief that systems of thought can be rationally criticized and evaluated although concrete proof of such a system is impossible. Popper wrote about critical rationalism in his work, The Open Society and its Enemies Volume 2.

Critical rationalism is thought as the third alternative of two other philosophies: strong rationalism and fideism. Fideism does not require a system of thought to be analyzed, while strong rationalism requires a proof to be shown.

Sir Hans Adolf Krebs David Deutsch