Suppose – rather reasonably – that soups which taste like garlic have garlic in them. You observe two people eating soup; one of them says to the other, “There is no garlic in this soup.” Do you think it’s likely that the soup taste like garlic?
If you said yes, then congratulations! You’ve just committed a logical fallacy (from the premise “if p then q” and “not q,” you have inferred p) so absurd that it’s only very recently been given a name. But don’t feel bad – this absurd inference, known as modus shmollens, can actually be elicited from a majority of adult human subjects when the situations are just right.
One such situation was demonstrated by Bonnefon & Villejoubert in 2007. They point out that, conversationally, human speakers are likely to make negative statements when they will correct the erroneous inference of a listener. That is, unless there is a good reason to believe (for example) that it might be snowing, there is little reason to state that it is not snowing.
In this example, why might a speaker believe that it might be snowing? One straightforward possibility is that both the speaker and listener have access to some other information – information we might call “p” – that supports the inference that it is snowing – which we might in turn call “q”. So, in a case where a speaker does bother to say that it is not snowing, or that a soup doesn’t taste like garlic (i.e., “not q”), one might intuitively guess that p is in fact true. Indeed, why else would the speaker bother to negate q?
Bonnefon & Villejoubert gave 60 young adults a series of situations just like this, which varied in whether the conditional “if p then q” premise was explicit in the situation or merely implicit, and whether the categorical “not q” premise was framed as an utterance by a human speaker or merely a fact of the world. In the situation where both the conditionals were explicit and the categorical premises were utterances, 55% of undergraduates actually endorsed the modus shmollens inference with high confidence. In a second experiment, the number was even higher – 75% of undergraduates endorsed the patently absurd modus shmollens inference.
To their credit, Bonnefon & Villejoubert do not tout this behavior as a new logical fallacy. Their view is much richer. They view their work as deriving from an infamous and often-criticized schism in psycholinguistics research, where “core” psycholinguistic phenomena are investigated independent of what are viewed as merely “pragmatic” phenomena which do not reflect a core language system. The obvious criticism of such an approach is that psycholinguistic theories which do not actually work in practice can be redefined so as to refer only to a small subset of situations where putatively “core” processes can be observed, and all other mere “pragmatic” phenomena swept under a rug. Bonnefon & Villejoubert suggest that for such an approach to be viable, we must take those pragmatic phenomena seriously as well, and begin to derive novel, falsifiable predictions based on them. As such, their demonstration of the problematic modus shmollens inference represents not merely a surprising and counterintuitive addition to the list of logical fallacies regularly committed by humans, nor merely insight into the context dependence of such fallacies, but also represents a more comprehensive approach to psycholinguistic theorizing.