 Much in the spirit of C. I. Lewis, Klein and Warfield illustrated their argument referring to a detective story (the so-called “Dunnit example”). It turns out that this example is unnecessarily complex and that the main point can be illustrated by reference to a simpler case (borrowed from computer science where it is used to exemplify the concept of non-monotonic inference). Suppose that you are told by one source, Jane, that Tweety is a bird and by another source, Carl, that Tweety cannot fly. The resulting information set \(S = \langle\)“Tweety is a bird”, “Tweety cannot fly”\(\rangle\) is not particularly coherent from an intuitive standpoint. Nor is it coherent from the point of view of Lewis’s definition: assuming one of the items true decreases the probability of the other. At this point, it would be reasonable to conjecture that either Jane or Carl is not telling the truth. However, upon consulting a further source, Rick, we receive the information that Tweety is a penguin. The new set \(S' = \langle\)“Tweety is a bird”, “Tweety cannot fly”, “Tweety is a penguin”\(\rangle\) is surely more coherent than \(S\). In explaining the previous anomaly, the information supplied by Rick contributes to the explanatory coherence of the set.