There are many versions of the Duhem-Quine thesis or problem. What Duhem said was, no verification of hypotheses is possible, and not even refutation, since the refuting evidence is not proven. Popper agreed and said, evidence refutes a theory to the contrary as long as it is endorsed. Duhem argued against the realist reading of theories as it is metaphysical. Quine and Popper disagreed with this. Kuhn renamed the thesis incommensurability, but he rejected both the realist view of scientific theories and the opposite view of them. It is not clear whether he offered any alternative view.