Modeling Two Kinds of Reasoning

This research addressed how inductive reasoning and deductive reasoning are related. We directly compared the ideas that the same cognitive mechanisms are applied to both types of judgments and that different processes lead induction and deduction to use different information. In an experiment, subjects either judged inductive strength or deductive validity, for a common set of arguments. A finding from Heit and Rotello (2005), greater sensitivity to validity in the deduction condition, was replicated. A new finding was greater sensitivity to number of premises for induction. The results were analyzed using signal detection theory (SDT) and receiver operating characteristic (ROC) curves, and modeled using both one-dimensional and multidimensional versions of SDT. The one-dimensional model could not capture differential sensitivity to number of premises. A successful model for the entire pattern of results assumed two underlying dimensions, deductive correctness and associative strength, with different proportions comprising either induction or deduction judgments.