"Rationality" in Popper's Philosophy of Science

In recent decades، rationality has become one of the important and controversial issues in the intellectual circles. There are many philosophers who have put (and still put) under question the status of reason and human rationality. Among those who believe in human reason is Popper. To show reason''s ability، he rejects positivism and justifying approaches totally; and، designing falsificationist philosophy of science، he confirms critical rationality and attaches emphasis to it. In the present article، at first، Popper''s rationality together with its important and constructive elements are inferred and reconstructed and، then، success and consistence of Popper''s positions are studied and assessed. The main conclusion of the present article is that it is impossible to completely reject positivist and justifying approaches and provide an absolutely negativist and critical epistemology.