 As an illustration, consider Kitcher’s treatment of the problem of explanatory asymmetries (recall  Section 2.5).  Our present explanatory practices—call these P—are committed to the idea that derivations of a flagpole’s height from the length of its shadow are not explanatory. Kitcher compares P with an alternative systemization in which such derivations are regarded as explanatory. According to Kitcher, P includes the use of a single “origin and development” (OD) pattern of explanation, according to which the dimensions of objects-artifacts, mountains, stars, organisms etc. are traced to “the conditions under which the object originated and the modifications it has subsequently undergone” (1989: 485). Now consider the consequences of adding to P an additional pattern S (the shadow pattern) which permits the derivation of the dimensions of objects from facts about their shadows. Since the OD pattern already permits the derivation of all facts about the dimensions of objects, the addition of the shadow pattern S to P will increase the number of argument patterns in P and will not allow us to derive any new conclusions. On the other hand, if we were to drop OD from P and replace it with the shadow pattern, we would have no net change in the number of patterns in P, but would be able to derive far fewer conclusions than we would with OD, since many objects do not have shadows (or enough shadows) from which to derive all of their dimensions. Thus OD belongs to the explanatory store, and the shadow pattern does not. Kitcher’s treatment of other familiar problem cases is similar. For example he claims that explanations that contain irrelevancies (such as Salmon’s birth control pills case are less unifying than competing explanations that do not contain such irrelevancies. 