Nonmonotonic Reasoning and Causation: Comment

In a recent issue of Cognitive Science, * Yoav Shoham (1990) proposed a theory of causation based on a nonmonotonic logic of temporal knowledge. It is the purpose of this commentary to show that Shoham’s procedure is essentially isomorphic with a theory of causal ordering that requires no special nonmonotonic logic. Although this latter causal ordering theory is compatible with the requirement that causes precede their effects, it can also be used to describe systems in which causes and effects are simultaneous. This discussion will employ a version of the causal ordering theory that uses Boolean truth functions of sentences (Simon, 1952; reprinted in Simon, 1977, chap. 2.2) rather than the more famliar version that uses mathematical functions of real variables (Simon, 1953; reprinted in Simon, 1977, chap. 2.1) as the material of construction. This will make the relation to Shoham’s theory easier to see. The discussion here will be largely informal; the formalities are easily supplied by reference to the original articles by Shoham (1990) and Simon (1952, 1953).