 A final and especially important qualification to the general recipe for realism described above comes in the form of a number of variations. These species of generic realism can be viewed as falling into three families or camps: explanationist realism; entity realism; and structural realism. There is a shared principle of speciation here, in that all three approaches are attempts to identify more specifically the component parts of scientific theories that are most worthy of epistemic commitment. Explanationism recommends realist commitment with respect to those parts of our best theories—regarding (unobservable) entities, laws, etc.—that are in some sense indispensable or otherwise important to explaining their empirical success—for instance, components of theories that are crucial in order to derive successful, novel predictions. Entity realism is the view that under conditions in which one can demonstrate impressive causal knowledge of a putative (unobservable) entity, such as knowledge that facilitates the manipulation of the entity and its use so as to intervene in other phenomena, one has good reason for realism regarding it. Structural realism is the view that one should be a realist, not in connection with descriptions of the natures of things (like unobservable entities) found in our best theories, but rather with respect to their structure. All three of these positions adopt a strategy of selectivity, and this and the positions themselves are considered further in  section 2.3.