The paper focuses on the explanation of one of the central problems of Popper’s philosophy of science - on the problem of criticism in various forms. Popper accepts Humean scepticism about induction, taking on board the consequence that this means that we can never know whether any universal theory is true. His scepticism runs deep, but he thinks he can base an account of scientific rationality on negative activity of attempting to disapprove theories. But criticism, freedom and rationality are central to Popper’s views on politics and open society. Science and politics, then are ideally to be characterized by an admission of our ignorance and by attempt to weed out false theories and to remedy the negative effects of our policies. The criticizing environment can attack our theories, which die in our stead. Popper’s project is the construction of rational model of science - science is the paradigm of institutionalized rationality, science has a special form of rationality embodied in the methods of science. His fallibilism is based on rejecting all non-deductive arguments.