Although the subjective conceptualisation of necessity parallels the formal definition; the subjective concept of sufficiency is different, less stringent than the formal concept. The Rationality 2-criterion dictated by normative theories is not suited to evaluate an everyday, Rationality-1 way of thinking. To give an example; smoking causes lung cancer. What would be expected when asked whether smoking is a sufficient cause for lung cancer? Because most people know smokers who did not get lung cancer, smoking can formally not be considered as a sufficient condition.
However, it is commonly known that smoking significantly increases the probability of getting lung cancer. This graded, positive relationship between cause and effect can be sufficient to label the cause as sufficient for the effect. Another group was asked whether it is possible that the effect does not follow the cause sufficient and that the cause does not precede the effect necessary.
Surprisingly, there was a considerable number of sentences where the majority of participants said that it was possible that the cause was not followed by the effect while at the same time participants still considered the cause sufficient for the effect. When we analyse the relevance and occurrence of both dimensions for everyday situations, we can suggest a possible reason. It has already been shown that the search for necessary causes is triggered in case of an undesired effect, while the search for a sufficient cause is triggered in case of a desired effect Lewicka, ; In case the effect is not desired, it is important to find a way of categorically preventing this effect.
If people know of a necessary precondition for the effect, the total absence of this precondition serves the purpose. However, for a desired effect it can be interesting to be merely able to augment the probability of this effect taking place. This can already reveal that it can be more adaptive to consider sufficiency in gradual terms and necessity in categorical terms.
It is often stated that the subjective levels of necessity and sufficiency predict the reasoning performance, but it remains yet to be tested whether it is the perceived levels of necessity and sufficiency that are reflected in the reasoning results rather than the objective levels that are manipulated by the researchers. They found that effects on inference acceptance rates are not always mediated by effects in the subjective necessity and sufficiency ratings.
The Logic of Sufficiency
They suggest that participants do not base their inferences on their assessment of the cause as necessary and sufficient. The question then remains why the objective levels of necessity and sufficiency have such a pervasive impact on the reasoning results, even when abstract premises are used. Although we only considered unicausal relations, we found evidence corroborating this claim: To verify sufficiency participants verify only one gradual relation, whereas for necessity the criterion is more stringent all-or-none and consists of two indications.
We do not know whether both indicators of necessity are used to assess the status of a cause, but it was found that the recognition of the first model is insufficient to conclude that a cause is necessary. Taken together this corroborates the finding that necessity is more complex than sufficiency. It seems to be more ecologically valid to define sufficiency in terms of for instance the likelihood that the cause brings about the effect, rather than in terms of an all-or-none property. When investigating the effect of the necessity and sufficiency of the cause on causal reasoning or decision making, researchers should stop at the thought of a valid operationalisation of these constructs.
A look at how reasoners understand the central theoretical concepts can avoid theoretical aberrations. If you heat the green sticky substance, then it turns light pink. If the small white animals are exposed to sunlight, then they die. If you drop these pearly pebbles, then they break in two. If you drink the blue fluid, then your head starts spinning. If you pull a bright yellow leaf from this plant, then there appears a black bud. If you boil these sweet tasting fruits, then they become bitter tasting. If the purple gas adds to the red gas, then there is an explosion.
If two of these orange marbles touch, then a poisonous smoke evaporates from them. If the treacly black stuff is stirred, then the stuff becomes glassy. Mental models in conditional reasoning and working memory. Thinking and Reasoning, 5 , Bindra, D. Journal of Experimental Psychology: General, , Brennan, A. Necessary and sufficient conditions. Byrne, R. Counterexamples and the suppression of inferences. Journal of Memory and Language, 40 , Cummins, D.
Memory and Cognition, 23, Conditional reasoning and causation. Edgington, D. On conditionals. Mind, , Evans, J.
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Contents - Next document. Outline Experiment 1. Interpretation of sufficiency and necessity. Subjective versus objective sufficiency and necessity. Appendix: Different contexts used for Experiment 2. Full text PDF Send by e-mail. Table 2 : Number of participants that included the following models in their definitions of necessity, sufficiency, non-necessity and non-sufficiency Zoom Original jpeg, 24k.
Zoom Original jpeg, 16k. Zoom Original jpeg, 24k. Truth-table task for investigating the necessity and sufficiency interpretation Zoom Original jpeg, 16k. Zoom Original jpeg, 14k.