Academic journal article Canadian Journal of Experimental Psychology

Content and Strategy in Syllogistic Reasoning

Academic journal article Canadian Journal of Experimental Psychology

Content and Strategy in Syllogistic Reasoning

Article excerpt


Syllogistic reasoning has been investigated as a general deductive process (Johnson-Laird & Byrne, 1991; Revlis, 1975; Rips, 1994). However, several studies have demonstrated the role of cognitive strategies in this type of reasoning. These strategies focus on the method used by the participants (Ford, 1995; Gilhooly, Logie, Wetherick, & Wynn, 1993) and strategies related to different interpretations of the quantified premises (Roberts, Newstead, & Griggs, 2001). In this paper, we propose that content (as well as individual cognitive differences) is an important factor in inducing a certain strategy or method for syllogistic resolution. Specifically, we suggest that syllogisms with a causal conditional premise that can be extended by an agency premise induce the use of a conditional method. To demonstrate this, we carried out two experiments. Experiment 1 provided evidence that this type of syllogism leads participants to draw the predicted conditional conclusions, in contrast with control content syllogisms. In Experiment 2, we demonstrated that the drawing of conditional conclusions is based on a causal conditional to an agent representation of the syllogism premises. These results support the role of content as inducing a particular strategy for syllogistic resolution. The implications of these results are discussed.

Syllogisms are arguments from two premises to a conclusion. Both premises and conclusion are statements of one of four types or moods: "All of the A are B" (A), "Some of the A are B" (I), "None of the A are B" (E), and "Some of the A are not B" (O). Each statement in the premises contains two terms: One term, the middle term (B), occurs in both premises, while the other two (A and C) are known as the end terms. The syllogistic conclusion relates the end terms by means of the middle term. For example,

All bricklayers are mechanics,

All chemists are bricklayers

Conclusion: All chemists are mechanics.

The arrangement of the end and middle terms in each of the premises gives rise to a four-way classification known as the figure of the syllogisms (see Johnson-Laird & Byrne, 1991).

The combination of the figure of the syllogisms and its mood gives rise to a great number of different syllogisms of which only a few have a propositionally valid conclusion (logically correct), that is to say, a conclusion necessarily derived from the premises.

Among the several tasks against which theories of reasoning are benchmarked, categorical syllogisms are of considerable importance. Different theories have been proposed to describe the process of syllogistic reasoning. Each one describes a different method for syllogistic resolution. In this respect, it is relevant to distinguish a heuristic method as proposed by the probabilistic heuristic model (Chater & Oaksford, 1999). This method suggests that people base their answers on the action of fast and frugal heuristic performing on the surface features of the problems (rather than attempt to reason by representing the information). These heuristics considerably reduce the cognitive demands of the task, but at the expense of resulting in systematic errors. The mental models method (Johnson-Laird & Byrne, 1991) requires a multistep process requiring information to be represented and transformed internally by means of mental models. The spatial method suggests that syllogisms are represented by means of Euler circles, and the action of the appropriate procedures enables the conclusion to be drawn (Ford, 1995; Stenning & Yule, 1997). In the rule-based method (Rips, 1994), the premises are represented as propositions and a group of diverse rules of inference are applied to them step by step in order to produce the conclusion, or evaluate a given conclusion. The conditional method considers that syllogisms are conditional inferences and for any individual conclusion, one premise supplies the conditional and the other the source of the atomic input to the conditional rule (Ford; Stenning & Yule). …

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