  In this latter case, the deductive extremists, in their mathematical zeal, seem to forget that cosmology, after all, should have some relation to observation: “To them all that is of interest in a theory is its logical character, not its relevance to the interpretation of observational data.” Obviously, this danger must be avoided: according to Bondi, deductivism can be a scientific approach in cosmology only if its postulates (or axioms) are candidates for disproof. 