1 A Bayesian Analysis of Some Forms of Inductive Reasoning Evan Heit University of Warwick In Rational Models of Cognition, M. Oaksford & N. Chater (Eds.), Oxford University Press, 248- 274, 1998. Please address correspondence to: Evan Heit Department of Psychology University of Warwick Coventry CV4 7AL, United Kingdom Phone: (024) 7652 3183 Email:
[email protected] 2 One of our most important cognitive goals is prediction (Anderson, 1990, 1991; Billman & Heit, 1988; Heit, 1992; Ross & Murphy, 1996), and category-level information enables a rich set of predictions. For example, you might not be able to predict much about Peter until you are told that Peter is a goldfish, in which case you could predict that he will swim and he will eat fish food. Prediction is a basic element of a wide range of everyday tasks from problem solving to social interaction to motor control. This chapter, however, will focus on a narrower range of prediction phenomena, concerning how people evaluate inductive “syllogisms” or arguments such as the following example: Goldfish thrive in sunlight --------------------------- Tunas thrive in sunlight. (The information above the line is taken as a premise which is assumed to be true, then the task is to evaluate the likelihood of the conclusion, below the line.) Despite the apparent simplicity of this task, there are a variety of interesting phenomena that are associated with inductive arguments. Taken together, these phenomena reveal a great deal about what people know about categories and their properties, and about how people use their general knowledge of the world for reasoning.