Negations without "not" : alternative forms of negation and contrast classes in conditional inference

Vance, James R. H. (2018) Negations without "not" : alternative forms of negation and contrast classes in conditional inference. Doctoral thesis, Birkbeck, University of London.

Abstract

This thesis explored the role of negation in conditional reasoning by looking at how different types of negation affected responses to reasoning questions. Previous research has observed several systematic biases in conditional reasoning with negations (Manktelow, 2012). Prior reasoning research has looked at negation as a simple logical operator. However, negation can take a range of forms and provide different implications (Horn, 1989). These experiments tested the effect of different types of negation on conditional reasoning. The first set of experiments looked at how using different types of negation in propositions affected people’s probability ratings of those propositions. The three experiments identified differences when using several different types of negation. However, the differences observed were small. These results confirmed that people do take different implications from different types of negation. The second set of four experiments used an extension of Evans’ (1977) conditional inference paradigm to compare two types of negation (using “not” and affix “un-”). The experiments looked at whether responses reflected the different probabilistic implications of those negative forms. Any effect of different types of negation appears overwhelmed by plausibility and other material effects. Broadly these results provide are consistent with probabilistic models of reasoning. However, inconsistencies in the results suggest further work is necessary to rule out other models. The final set of three experiments used a novel learning task to test the effect of frequency information on inference endorsement tasks. The first experiment confirmed Oaksford and Chater’s (2007) prediction of MP inference suppression when implicit negation is used instead of “not” negation and participants are provided with appropriate frequency information. Two further experiments confirmed that this effect was the result of the frequency information and extended it to AC, DA and MT inferences. These results provide support for a probabilistic approach to reasoning.

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