 Explanatory Asymmetries. There are many cases in which a derivation of an explanandum E from a law L and initial conditions I seems explanatory but a “backward” derivation of I from E and the same law L does not seem explanatory, even though the latter, like the former, appears to meet the criteria for successful DN explanation. For example, one can derive the length s of the shadow cast by a flagpole from the height h of the pole and the angle θ of the sun above the horizon and laws about the rectilinear propagation of light. This derivation meets the DN criteria and seems explanatory. On the other hand, the following derivation from the same laws also meets the DN criteria but does not seem explanatory: