 Philosophy of science became professionally consolidated in the 1950s around a positivist orthodoxy that may be characterized by the following set of commitments: a syntactic formal approach to theories, logical deductions and axiomatic systems, a distinction between theoretical and observational vocabularies, and empirical generalizations. Unity and especially reduction have been understood in those terms; specific elements of the dominating accounts would stand and fall with the attitudes towards the elements of the orthodoxy mentioned above. First, a reminder: Reductionism must be distinguished from reduction. Reductionism is the adoption of reduction as the global ideal of a unified structure of scientific knowledge and a measure of its progress towards that ideal. As before, I will consider methodological aspects of unity as an extension of epistemological matters, insofar as methodology serves epistemology.