 There are several even simpler examples that illustrate the need to include explicitly causal information in the input to defeasible reasoning. Consider, for instance, this problem of Judea Pearl’s (Pearl 1988): if the sprinkler is on, then normally the sidewalk is wet, and, if the sidewalk is wet, then normally it is raining. However, we should not infer that it is raining from the fact that the sprinkler is on. (See Lifschitz 1990 and Lin and Reiter 1994 for additional examples of this kind.) Similarly, if we also know that if the sidewalk is wet, then it is slippery, we should be able to infer that the sidewalk is slippery if the sprinkler is on and it is not raining.