Two weeks ago Edouard Machery argued against the idea that common sense is a good guide to reality. Common sense relies on intuition; and intuitions are unreliable, vary greatly across cultures and are sensitive to seemingly irrelevant factors such as the wording of a particular thought experiment. This week Nevin Climenhaga challenges this view, arguing that we can have good intuitions and bad ones, and that there are legitimate ways of sorting reliable from unreliable ones.

Analytic philosophers frequently appeal to intuitions as evidence for philosophical claims. For example, it seems to me that knowledge can be extended by deduction and inference: if Alice knows that Bob is 25, Alice can deduce, and in so doing come to know, that Bob is over 21. On the basis of this felt intuition, I conclude that knowledge can always be extended by deduction: if you know Q and know that Q entails R, then you’re able to come to know R by deducing it from Q.

SUGGESTED READING Common sense is not a good guide to reality By Edouard Machery

Here I use my intuition about knowledge as evidence for a philosophical claim about knowledge. Using intuitions as evidence is common in analytic philosophy. But in recent years this practice has come under criticism (see Edouard Machery’s). Skeptics about the reliability of intuitions argue that we have no good reason to think the way things seem to us reflect the way things are, bolstering their case with experiments showing how our intuitions can be impacted by cognitive biases (such as the order that different questions are presented in) and vary according to seemingly irrelevant demographic differences (such as sex, socioeconomic status, or cultural background).

In light of these challenges, how reasonable is it for philosophers to rely on intuitions as evidence? We should be wary of overly general conclusions here. Like other kinds of evidence—such as visual experience, testimony, or the results of scientific experiments—some intuitions have more evidential value than others. The key question to ask in a particular case is this: how much more likely am I to have this intuition if its content is true than if its content is false? Bayes’ theorem tells us that the more likely it is that I would have an intuition that P if P is true than otherwise, the more this intuition raises the probability of P.

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