While this referentialist response to the incommensurability thesis was initially framed in Fregean terms (Scheffler 1967), it received further impetus from the work of Kripke (1980) and Putnam (1975b), which argued that reference could be achieved without anything akin to Fregean sense and that the natural kind terms of science exemplified this sense-free reference. In particular, causal theories of reference permit continuity of reference even through fairly radical theoretical change. (They do not guarantee continuity in reference, and changes in reference can occur on some causal theories, e.g. Gareth Evans’s (1973). Arguing that they do occur would require more, however, than merely pointing to a change in theory.  Rather, it seems, cases of reference change must be identified and argued for on a case by case basis.) Therefore, if taken to encompass terms for quantities and properties (such as ‘mass’), the changes that Kuhn identified as changes in meaning (e.g. those involved in the shift from Newtonian to relativistic physics) would not necessarily be changes that bear on reference, nor, consequently, on comparison for nearness to the truth.  The simple causal theory of reference does have its problems, such as explaining the referential mechanism of empty theoretical terms (e.g.caloric and phlogiston) (c.f. Enç 1976, Nola 1980). Causal-descriptive theories (which allow for a descriptive component) tackle such problems while retaining the key idea that referential continuity is possible despite radical theory change (Kroon 1985, Sankey 1994).