What Should Default Reasoning be, by Default?

Abstract

This is a position paper concerning the role of empirical studies of human default reasoning in the formalization of AI theories of default reasoning. We note that AI motivates its theoretical enterprise by reference to human skill at default reasoning, but that the actual research does not make any use of this sort of information and instead relies on intuitions of individual investigators. We discuss two reasons theorists might not consider human performance relevant to formalizing default reasoning: (a) that intuitions are sufficient to describe a model, and (b) that human performance in this arena is irrelevant to a competence model of the phenomenon. We provide arguments against both these reasons. We then bring forward three further considerations against the use of intuitions in this arena: (a) it leads to an unawareness of predicate ambiguity, (b) it presumes an understanding of ordinary language statements of typicality, and (c) it is similar to discredited views in other fields. We advocate empirical investigation of the range of human phenomena that intuitively embody default reasoning. Gathering such information would provide data with which to generate formal default theories and against which to test the claims of proposed theories. Our position is that such data are the very phenomena that default theories are supposed to explain.

The Case for Psychologism in Default and Inheritance Reasoning

“…We wish to draw out the psychologistic presupposition that lurks behind their work, and employ that as a justification for our empirical investigations. In Pelletier and Elio (1997) we canvassed numerous works by researchers in the field in order to discover their underlying justification for their investigations into non-monotonic logic. Here four sample quotations (out of very many) from this study:…”

“…More importantly, an individual's intuitions are not a reliable guide to how the population as a whole treats the phenomenon. In Pelletier and Elio (1997) we have investigated the various reasons researchers give for allowing their own intuitions to be their sole guide in this regard and for not engaging in large-scale investigations of how it is manifested in the population as a whole. We did not find any of these reasons very compelling, and recommended that researchers undertake such studies in order to determine the correct direction for their formal theories to follow.…”

On using human nonmonotonic reasoning to inform artificial systems

“…However, many people probably already know that speakers of Pennsylvanian Dutch are normally born in the US and they can quite easily ignore the other side of the argument. Pelletier and Elio's (1997;in press;Elio & Pelletier, 1993 call for more studies on human nonmonotonic reasoning and their claim that nonmonotonic reasoning is psychologistic should be seen as separate issues. They will thus be treated separately in the second and third sections.…”

“…There are five main reasons why one might agree with Pelletier and Elio (1997;in press;Elio & Pelletier, 1993 on the need to study human nonmonotonic reasoning: a. The classic problems, such as (1) and (2), are often biased to already known answers and sometimes contain non-strict statements when the content is actually strict, thus eroding one's confidence that the intuitions of AI researchers about preferred responses would hold for the argument forms per se.…”

“…The AI community on nonmonotonic reasoning As Pelletier and Elio (1997;in press;Elio & Pelletier, 1993 note, AI researchers do not gather data on human reasoning when attempting to formalize their theories of nonmonotonic reasoning, but instead use their own intuitions. It seems it is assumed that for many problems the "correct" answer is obvious.…”