 In a similar spirit, notions of reduction are often characterized as being either ontological or epistemological. There is, again, no uniform use of these qualifications. For Oppenheim and Putnam (1958), epistemological reduction is a reduction that is “true in virtue of the meanings of the terms involved” (1958: 3), i.e., reduction that is tied to analysis in the spirit of  A Priori Reduction-2;  this use, however, is relatively rare. First of all, it will prove useful to draw a distinction between epistemological and ontological forms of reductionism.