Proceedings of the Annual Meeting of the Cognitive Science Society

When one looks at transcripts of people answering questions or carrying on dialogues about everyday matters, their comments are filled with plausible inferences -- inferences that are not certain, but that make sense. Often, in forming these inferences, generalizations are made that are equally uncertain, but are nevertheless useful as a guide to their reasoning. This paper describes some extensions to our earlier description of a core theory of plausible reasoning (Collins and Michalski, 1989), based in large part on a recent protocol study. The primary focus is on the inductive inference patterns people use to form plausible generalizations, weakly held beliefs based on few examples. W e also show how the model was extended to deal with plausible inferences involving continuous quantities and inequalities.