Guy Politzer

A Developmental Investigation of Processing Costs in Implicature Production

Much developmental work has been devoted to scalar implicatures. These are implicitly communicated propositions linked to relatively weak terms (consider how Some pragmatically implies Not all) that are more likely to be carried out by adults than by children. Children tend to retain the linguistically encoded meaning of these terms (wherein Some is compatible with All). In three experiments, we gauge childrens performance with scalars while investigating four factors that can have an effect on implicature production: (i) the role of (the presence or absence of) distractor items; (ii) the nature of the task (verbal judgments versus action-based judgments); (iii) the choice of scalar expression (the French quantifier quelques versus certains); and (iv) the type of scale that contextualizes the weak utterance (the affirmative All versus the negative None). Experiment 1 replicated earlier findings showing that 9-year-olds are more likely than adults to consider as true statements such as Some turtles are in the boxes (uttered when all turtles are in the boxes) while employing the quantifier certains in a truth evaluation task containing multiple distractor items. The task in Experiment 2 increased implicature production across all ages (4-, 5-, and 7-year-olds as well as adults) but maintained the developmental effect while using quelques in an action-based task containing no distractor items. Experiment 3 showed that 9-year-olds are more likely to produce implicatures with quelques than they are with certains in the action task while adults are not affected by the choice of term. Overall, these results identify seemingly harmless task features that can prevent even older children (9-year-olds) from carrying out implicatures (e.g., through the inclusion of distractors) while also showing how implicature production among even young children (4- to 5-year-olds) can be facilitated by task features (e.g., the use of an action task) and without the introduction of special training.

Responses to inconsistent premisses cannot count as suppression of valid inferences

Byrne (1989) claims to have demonstrated that context can suppress valid inferences like modus ponens. If substantiated, the claim would refute the idea that valid inferences cannot be countermanded without contradiction, although implicatures and invited inferences can be (e.g., Braine & Rumain, 1981; Geis & Zwicky, 1971; Grice, 1975). That, in turn, would invalidate one of the few available methods for distinguishing between inferences that are intuitively necessary and those that are merely implicated or invited. Thus, on conditional reasoning problems, Rumain, Connell, and Braine (1983) found that the common fallacies known as “denying the antecedent” and “asserting the consequent” can be suppressed by a kind of modification of the problem that leaves modus ponens untouched. Markovits (1984, 1985) has reported similar results. Byrne claims that by an essentially similar maneuver one can cause subjects to reject instances of modus ponens. She concludes that this sort of experimental maneuver provides no more reason for thinking that subjects have an inference rule for modusponens than that they have inference rules that generate the fallacies. We think that there are important differences between the problem modifications of Rumain et al. and of Byrne, and these lead us to dispute Byrne’s claims. In the experiment of Rumain et al. subjects reasoned about the content of a closed box. Some of the problems were ordinary conditional reasoning problems in that they presented a single conditional like:

Betting on conditionals

A study is reported testing two hypotheses about a close parallel relation between indicative conditionals, if A then B, and conditional bets, I bet you that if A then B. The first is that both the indicative conditional and the conditional bet are related to the conditional probability, P(B|A). The second is that de Finettis three-valued truth table has psychological reality for both types of conditional—true, false, or void for indicative conditionals and win, lose, or void for conditional bets. The participants were presented with an array of chips in two different colours and two different shapes, and an indicative conditional or a conditional bet about a random chip. They had to make judgements in two conditions: either about the chances of making the indicative conditional true or false or about the chances of winning or losing the conditional bet. The observed distributions of responses in the two conditions were generally related to the conditional probability, supporting the first hypothesis. In addition, a majority of participants in further conditions chose the third option, “void”, when the antecedent of the conditional was false, supporting the second hypothesis.

Deductive reasoning from uncertain conditionals.

This paper begins with a review of the literature on plausible reasoning with deductive arguments containing a conditional premise. There is concurring evidence that people presented with valid conditional arguments such as Modus Ponens and Modus Tollens generally do not endorse the conclusion, but rather find it uncertain, in case (1) the plausibility of the major conditional premise is debatable, (2) the major conditional premise is formulated in frequentist or probabilistic terms, or (3) an additional premise introduces uncertainty about the major conditional premise. This third situation gives rise to non-monotonic effects by a mechanism that can be characterized as follows: the reasoner is invited to doubt the major conditional premise by doubting the satisfaction of a tacit condition, which is necessary for the consequent to occur. Three experiments are presented. The first two aim to generalize the latter result using various types of conditionals and the last shows that performance in conditional reasoning is significantly affected by the representation of the task. This third point is discussed along with various other issues: we propose a pragmatic account of how the tacit conditions mentioned earlier are treated in plausible reasoning; the relationship of this account with the conditional probability view on conditional sentences is examined; an application of the same account to the Suppression Effect (Byrne, 1989) is proposed and compared with the counter-example availability explanation; and finally, some suggestions on how uncertainty could be implemented in a mental logic system are presented.

Belief revision and uncertain reasoning

When a new piece of information contradicts a currently held belief, one has to modify the set of beliefs in order to restore its consistency. In the case where it is necessary to give up a belief, some of them are less likely to be abandoned than others. The concept of epistemic entrenchment is used by some AI approaches to explain this fact based on formal properties of the belief set (e.g., transitivity). Two experiments were designed to test the hypothesis that contrary to such views, (i) belief is naturally represented by degrees rather than in an all-or-nothing manner, (ii) entrenchment is primarily a matter of content and not only a matter of form, and (iii) consequently prior degree of belief is a powerful factor of change. The two experiments used Elio and Pelletiers (1997) paradigm in which participants were presented with full simple deductive arguments whose conclusion was denied, following which they were asked to decide which premise to revise.

Uncertainty and the de Finetti tables

The new paradigm in the psychology of reasoning adopts a Bayesian, or probabilistic, model for studying human reasoning. Contrary to the traditional binary approach based on truth functional logic, with its binary values of truth and falsity, a third value that represents uncertainty can be introduced in the new paradigm. A variety of three-valued truth table systems are available in the formal literature, including one proposed by de Finetti. We examine the descriptive adequacy of these systems for natural language indicative conditionals and bets on conditionals. Within our framework the so-called “defective” truth table, in which participants choose a third value when the antecedent of the indicative conditional is false, becomes a coherent response. We show that only de Finettis system has a good descriptive fit when uncertainty is the third value.

When is a conclusion worth deriving? A relevance-based analysis of indeterminate relational problems

When is a conclusion worth deriving? We claim that a conclusion is worth deriving to the extent that it is relevant in the sense of relevance theory (Sperber & Wilson, 1995). To support this hypothesis, we experiment with “indeterminate relational problems” where we ask participants what, if anything, follows from premises such as A is taller than B, A is taller than C. With such problems, the indeterminate response that nothing follows is common, and we explain why. We distinguish several types of determinate conclusions and show that their rate is a function of their relevance. We argue that by appropriately changing the formulation of the premises, the relevance of determinate conclusions can be increased, and the rate of indeterminate responses thereby reduced. We contrast these relevance-based predictions with predictions based on linguistic congruence.

Reasoning and pragmatics

Language pragmatics is applied to analyse problem statements and instructions used in a few influential experimental tasks in the psychology of reasoning. This analysis aims to determine the interpretation of the task which the participant is likely to construct. It is applied to studies of deduction (where the interpretation of quantifiers and connectives is crucial) and to studies of inclusion judgment and probabilistic judgment. It is shown that the interpretation of the problem statements or even the representation of the task as a whole often turn out to differ from the experimenters assumptions. This has serious consequences for the validity of these experimental results and therefore for the claims about human irrationality based on them.

Reasoning, Judgement and Pragmatics

In psychological experiments on reasoning, participants are typically presented with premises which refer to general knowledge or which are integrated in an original scenario; then, either they are asked to derive what follows from the premises or they are provided with one or several conclusions and asked to decide whether or not these conclusions follow from the premises. There is always a logical argument underlying the premises and the conclusion, and the aim of such experiments is to study participants’ performance with respect to a theoretical model, either normative or, as is more usual nowadays, descriptive. The experiments on judgement do not differ much, except that they look more like a problem to solve, where the final question is a request for a comparison, a qualitative or a quantitative evaluation, and so on. The experiment may be administered orally during an interview with the experimenter, but more often it is administered in a written form, using paper and pencil or a computer. Given that there are two interlocutors engaged in a communication, a conversational analysis is appropriate, whether the presence of the experimenter is physically real or mediated by the support of the written messages.

Updating: A psychologically basic situation of probability revision

The Bayesian model has been used in psychology as the standard reference for the study of probability revision. In the first part of this paper we show that this traditional choice restricts the scope of the experimental investigation of revision to a stable universe. This is the case of a situation that, technically, is known as focusing. We argue that it is essential for a better understanding of human probability revision to consider another situation called updating (Katsuno & Mendelzon, 1992), in which the universe is evolving. In that case the structure of the universe has definitely been transformed and the revision message conveys information on the resulting universe. The second part of the paper presents four experiments based on the Monty Hall puzzle that aim to show that updating is a natural frame for individuals to revise their beliefs.