Are delusions rational?

by | Dec 8, 2022 | Blog posts

A few decades ago, the Harvard psychologist Brendan Maher made an unusual claim. People with delusions use the same rational process as non-delusional people. The distinction between being “psychotic” – that is, having delusions or hallucinations – and being non-psychotic was not qualitative, but quantitative. Delusional people are just more irrational than normal people. This experimental result is confirmed with the many studies on the cognitive biases of normal thinking, such as the famous example of confirmation bias (you believe a viewpoint based on your recent observations that confirm that viewpoint, while paying less attention to observations that don’t confirm that viewpoint).

A century ago, the famous psychiatrist and philosopher Karl Jaspers had laid out an opposite perspective: the “un-understandibility” criterion for delusions. Delusions were ideas which a clinician simply could not understand, no matter how hard he/she tried to do so. The clinician tried to empathize with the patient’s perspective as much as possible, but simply couldn’t. Where that line happened is where delusions began. Many have criticized Jaspers simplistically, saying that more or better empathy could explain many delusions. But Maher’s critique takes it even further: it’s not about empathy or trying to understand someone different than oneself; rather the same irrational process are used by everyone, just more or less.

The two features could be linked. Delusions are of two types, bizarre and non-bizarre. Non-bizarre delusions are rational and possible but simply wrong (the FBI is following me; that happens but probably not to me). Bizarre delusions are irrational and impossible (I’m a member of the CIA; my intestines are infected by Martians). Maher’s view could be restated as meaning that non-bizarre delusions meet all rationality criteria. Jaspers view could be restated as meaning that bizarre delusions are not understandable. The main mistakes of critics of Jaspers is that they make the easy critique of his view for non-bizarre delusions but they don’t address bizarre delusions. Jaspers himself didn’t make that distinction, but that doesn’t mean that we can’t do so. Similarly I don’t think Maher made the distinction about how his views applied to bizarre vs non-bizarre delusions. But we can.

In short, most delusions are non-bizarre, and Maher’s analysis applies: they are not qualitatively differen than normal thinking. They’re just more irrational to the point of being false. Some delusions are bizarre, and here Jaspers’ analysis applies: they are qualitatively different than normal thinking, and just metaphysically impossible.