This chapter explores the problem of method and truth as a challenge to epistemological aspects of the Alan Musgrave's scientific realism. Musgrave is one of the foremost contemporary defenders of scientific realism. He is also one of the leading exponents of Karl Popper's critical rationalist philosophy. Scientific realism enforces a sharp divide between method and truth. The problem of method and truth may be illustrated within the context of Popper's philosophy of science by means of the connection between corroboration and verisimilitude. Putnam illustrates the non-epistemic nature of metaphysical realist truth with the example of the ideal theory which would ultimately result if science were pursued to the ideal limit of inquiry. The standard argument for scientific realism is the so-called 'success argument', or, as Musgrave calls it, 'the Ultimate Argument'. The justificationist conception of rationality is the conception of rationality that underlies most traditional and contemporary thinking about rational belief.