 Alexander Rosenberg (1978; 1985: Ch. 4) argues that Mendelian properties supervene on molecular properties, i.e., that for any difference in Mendelian properties there is a difference in molecular properties. Thus, even if theory reduction is not available, the facts of Mendelian genetics can be ontologically reduced to facts of molecular genetics. Others describe this situation by observing that while token-token reduction is possible, type-type reduction is not to be had (Kimbrough 1979). Closer to a Kuhnian notion of incommensurability is Michael Ruse’s (1971) reconstruction, according to which the Mendelian gene and the molecular gene are incompatible concepts. One reason is that the former was treated as a unit of function, recombination, and mutation, while the latter is not. Furthermore, molecular genetics explains everything that is explained by Mendelian genetics and more; it has more explanatory power and is more accurate. Hence, according to Ruse, molecular genetics does not reduce, but replaces Mendelian genetics. Others defend the thesis that Mendelian genetics in its original version is reduced by molecular genetics (e.g., Goosens 1978).