 Now, there are three major accounts of reference and meaning that have been used, implicitly or explicitly, for the semantics of theoretical terms: (i) the descriptivist picture, (ii) causal and causal-historical theories and (iii) hybrid ones that combine descriptivist ideas with causal elements (Reimer 2010). Accounts of reference and meaning other than these play no significant role in the philosophy of science. Hence, we need to survey at least nine combinations consisting, first, of an abstract characterization of the nature of a theoretical entity (realist, non-realist and Pythagorean), and, second, a particular account of reference (descriptivist, causal and hybrid). Some of these combinations are plainly inconsistent and, hence, can be dealt with very briefly. Let us start with the realist view of theoretical entities.