 Traditional conventionalism, as exemplified in the work of Mach, Poincaré and Milhaud amongst others, holds that a “successful” science is one in which universal theories have assumed such explanatory critical mass that a convention emerges to pre-empt the possibility of their empirical refutation. This is strongly rejected by Popper, who differentiates his position from it by arguing that it is the acceptance of basic statements, rather than that universal theory, which is determined by convention and intersubjective agreement. For him, the acceptance or rejection of theory occurs only indirectly and at a higher investigative level, through critical tests made possible by the conventional acceptance of basic statements. As he puts it, “I differ from the conventionalist in holding that the statements decided by agreement are not universal but singular” (2002: 92). Simultaneously, however, he rejects any suggestion that basic statements are justifiable by direct experience: