We begin by highlighting some points related to Kuhn’s later thoughts on the incommensurability thesis and then show to what extent the standard version of the thesis given by the structuralist metatheory allows us to capture Kuhn’s ideas. Our main aim is to establish what constitutes the basis of comparability between incommensurable theories, even in cases of incommensurability with respect to theoretical and non-theoretical terms. We propose that comparability between incommensurable theories requires some connection between their respective ontologies that can (...) be captured by means of an ontological non-reductive relation. At this point, the structuralist notion of “echeloned partial substructure” may be of help. When the incommensurability is very drastic, the existence of ontological connections between the theories involved may only be evident by common terms of their non-characteristic vocabularies. So, this notion of non-characteristic vocabulary becomes relevant in our proposal. (shrink)