Paolo Legrenzi

Reasoning from inconsistency to consistency.

This article presents a theory of how individuals reason from inconsistency to consistency. The theory is based on 3 main principles. First, individuals try to construct a single mental model of a possibility that satisfies a current set of propositions, and if the task is impossible, they infer that the set is inconsistent. Second, when an inconsistency arises from an incontrovertible fact, they retract any singularly dubious proposition or any proposition that is inconsistent with the fact; otherwise, they retract whichever proposition mismatches the fact. A mismatch can arise from a proposition that has only mental models that conflict with the fact or fail to represent it. Third, individuals use their causal knowledge-in the form of models of possibilities-to create explanations of what led to the inconsistency. A computer program implements the theory, and experimental results support each of its principles.

Children's reasoning on conditional promises and permissions

Abstract The responses of seventy-two 12-year-old children to a selection and evaluation task were compared in four conditions involving different social rules. The results show that the childrens strategies in searching for possible violators depend on the type fo the rule being tested (e.g., permission vs. promise), and in the knowledge of the goals of the possible violator (e.g., selfish vs nepotistic). It is concluded that selection and evaluation performance which could be judged as corret according to a logical criterion are due neither to the use of falsificatin strategies, nor to a generic facilitating social context effect. The role of pragmatic factors in childrens deductive reasoning is discussed in relation to the adult literature on the topic.

The Influence of Linguistic Form on Reasoning: The Case of Matching Bias

A well-established phenomenon in reasoning research is matching bias: a tendency to select information that matches the lexical content of propositional statements, regardless of the logically critical presence of negations. Previous research suggested, however, that the effect might be restricted to reasoning with conditional statements. This paper reports two experiments in which participants were required to construct or identify true and false cases of propositional rules of several kinds, including universal statements, disjunctions, and negated conjunctions. Matching bias was observed across all rule types but largely restricted to problems where participants were required to falsify rather than to verify the rules. A third experiment showed a similar generalization across linguistic forms in the Wason selection task with only if conditionals substituted for universals. The results are discussed with reference to contemporary theories of propositional reasoning.

Models of Consistency

This article presents a theory of how individuals detect whether descriptions of an entity are consistent or inconsistent. The theory postulates that individuals try to construct a mental model of the entity in which all the propositions are true. If they succeed, they infer that the description is consistent; otherwise, they infer that it is inconsistent. We report three experiments that corroborated the theory. Experiment 1 confirmed that evaluating consistency is easier when an initial model suffices than when reasoners have to find an alternative model. Experiment 2 established the occurrence of illusory inferences about the properties of entities. Experiment 3 showed that the illusions correspond to mental models of the assertions, even when these models are wrong because they fail to represent what is false.

How We Detect Logical Inconsistencies

How do individuals detect inconsistencies? According to the theory described in this article, they search for a possibility represented in a mental model, in which each proposition in a description is true. If they find such a possibility, the description is consistent; otherwise, it is inconsistent. Evidence corroborates the theory. The evaluation of consistency is easy when the first possibility generated from the start of a description fits later propositions in the description; it is harder when this possibility does not fit later propositions, and individuals have to look for an alternative possibility. The theory postulates that models represent what is true, not what is false. As a result, individuals succumb to systematic illusions of consistency and of inconsistency.

Mental representation and hypothetico-deductive reasoning: The case of the THOG problem

SummaryThis article reports three experiments that deal with the source of the difficulty of Wasons (1977) THOG problem. The solution of this problem demands both the postulation of hypotheses and a combinatorial analysis of their consequences. Experiment 1 showed that the generation of the hypotheses is not in itself sufficient to solve the problem. Experiment 2 showed that a version presenting a plausible context for separating the level of data from that of hypotheses produced a better performance than both the original abstract version and a thematic version lacking the plausible context separating the levels. Experiment 3 gave evidence that this context can produce facilitation even with the geometric material of the classic version. This experiment also showed that a pictorial presentation of data and a verbal presentation of hypotheses affect performance negatively. The results demonstrate the role of problem representation in problem solving, and, in particular, the role of homogeneity in representing data and hypotheses in hypothetico-deductive reasoning.

The psychology of reasoning about preferences and unconsequential decisions

People can reason about the preferences of other agents, and predict their behavior based on these preferences. Surprisingly, the psychology of reasoning has long neglected this fact, and focused instead on disinterested inferences, of which preferences are neither an input nor an output. This exclusive focus is untenable, though, as there is mounting evidence that reasoners take into account the preferences of others, at the expense of logic when logic and preferences point to different conclusions. This article summarizes the most recent account of how reasoners predict the behavior and attitude of other agents based on conditional rules describing actions and their consequences, and reports new experimental data about which assumptions reasoners retract when their predictions based on preferences turn out to be false.

Contract Proposals A Sketch of a Grammar

In this paper we analyse the way in which contract proposals can be expressed in order to be considered as well formed. We limit ourselves to a micro-world containing two parties in interaction (a Speaker and a Hearer), and two utility values (positive and negative) attached to the exchanged goods. A contract is defined as well formed if the exchange would result in an increase in utility for both parties. In that micro-world, 64 forms of contract proposals are formally definable. However, only 32 forms are permissible to express a well-formed contract. These forms convey the same meaning but differ in their conditions of use. Two of them are identified as more basic (canonical) forms to which all the others can be reduced from a semantic point of view. A partition of the 32 well-formed proposals into two subsets of equal size can be made on the basis of these two canonical forms. One subset is made of forms that can degenerate into non-contractual forms (threats) provided a condition on one of the utilities is satisfied, whereas the forms of the other subset cannot degenerate.

Decision Makers Use Norms, Not Cost-Benefit Analysis, When Choosing to Conceal or Reveal Unfair Rewards

We introduce the Conceal or Reveal Dilemma, in which individuals receive unfair benefits, and must decide whether to conceal or to reveal this unfair advantage. This dilemma has two important characteristics: it does not lend itself easily to cost-benefit analysis, neither to the application of any strong universal norm. As a consequence, it is ideally suited to the study of interindividual and intercultural variations in moral-economic norms. In this paper we focus on interindividual variations, and we report four studies showing that individuals cannot be swayed by financial incentives to conceal or to reveal, and follow instead fixed, idiosyncratic strategies. We discuss how this result can be extended to individual and cultural variations in the tendency to display or to hide unfair rewards.

Psychologistic Aspects of Suppes’s Definition of Causality

From the point of view of the analysis of everyday reasoning about causality, the psychologists’ research has shown the relevance but also the insufficiency of Suppes’s definition of causality. Neither the probabilistic definition of causality nor the theory of rational choice can fully explain the data obtained with experiments on counterfactual reasoning and decisions. We have tried to show a link between judgements of causality and decision making. It seems necessary to analyze the type of decision on which an action is based in order to judge the causal role of this action. The data obtained by psychologists in different domains, such as perception and thinking, support both the realistic and the constructivistic positions discussed by philosophers in relation to the nature of causality.