The main theme is that theorizing serves empirical prediction. This is used as the core of a counter to contemporary anti-realist arguments. Different versions of the thesis that data underdetermines theory are identified and it is shown that none which are acceptable differentiates between theory selection and prediction. Criteria sufficient for the former are included amongst those necessary for the latter; and obviously go beyond mere compatibility with data.Special attention is given to causal process theories. It is argued that the (...) only empirically equivalent alternatives which can be constructed to any theory of this kind must be parasitic on that theory; so a choice for the original theory can not be avoided. Once this is established, a positive case for taking a realist position can be developed. (shrink)