A formalization of a phenomenon is elaboration tolerant to the extent that it permits elaborations of the description without requiring completely redoing the basis of the formalization. In particular, it would be unfortunate to have to change the predicate symbols. Ideally the elaboration is achieved by adding sentences, rather than by changing sentences. Often when we add sentences we need to use some form of non-monotonic reasoning. This is because we often want to add information that we would previously have assumed was false. Unless we use non-monotonicity we would get inconsistency. In this paper we concentrate on the easier case when there is no need for non-monotonicity.
Natural language descriptions of phenomena seem to be more elaboration tolerant than any existing formalizations. Here are the two major kinds of elaboration tolerance that we examine in this paper.