Understanding Complex Concepts: Investigation of the Overextension Effect Using the Truth-Value Judgment Task

Abstract

This thesis is part of a larger scale project investigating how we understand complex concepts that are a conjunction of two simple categories (e.g. food that is also a plant). When we give our membership judgments in such complex categories, we often tend to overextend our linguistic categories: we agree to membership in the conjunction while disagreeing with membership in one of the constituent categories. This behavior is in contradiction with classical logic, that states that we can only agree with membership in the conjunction iff we agree with membership in both constituents. The effect that is described is widely known as the overextension effect. This thesis offers an insight into overextension data for Dutch, using novel items and categories. The subjects of this study (n=63) were asked to give their membership judgments of an item (e.g. bread) in two simple categories (e.g. food and plant) and in their conjunction (food that is also a plant). Two different analyses of the data show that the presence of the overextension effect in our data is greatly dependent on the assumptions that underlie our analysis: responses inconsistent with classical logic are the effect of people changing their minds about their judgment in a constituent category (M1) OR inconsistent responses are due to noise (M2). Based on the outcomes of the current experiment, we are not able to choose between these models. Further investigation of the origin of inconsistent responses is needed so that we may take another look at how we understand complex concepts and what is the role of overextension in this process.