As such, a realist position regarding existence in general is not vulnerable to positivist or empiricist critiques. In chapter three, the theory of retoduction is verified as a theory of scientific progress. It accounts for the activity of actual scientists, including the complex advances made by such notables as Newton and Galileo. McMullin's historical analysis of these figures, coupled with his deft handling of anti-realist and sociological critiques of scientific rationality, supports the ontological character of scientific rationality with the secured critical component from a historical study of science. In chapter four, the contemporary discipline of cosmology is treated as unique in illustrating the power of McMullin's theory of retroduction.
Cosmology is demonstrated as both an explanatory and a limit discipline in the natural sciences.
As such, it also fully exposes the presence of human values in scientific rationality, especially in light of the question of human destiny in a contingent universe. At this juncture, the God question attains its specificity in the science-theology dialogue. In chpater five, in line with the priority on faith emphasized in Polkinghorne's Gifford lectures, and given the theological implications of McMullin's development of a theory of scientific rationality, theology can claim a God-World relationship. The key step here is the distinction between the epistemological elements of scientific rationality and the unique role of the imagination in the act of understanding human understanding. This step is crucial for cohering an understanding an Augustinian theological outlook of a transcendent God with a position of critical realism that is the outcome of a full exploration of human rationality.