The Perils of Belief: Delusions Reexamined

Karl Jaspers' View of Delusions: The Essentialist Error

In more than a century of thinking about delusions, one result is clear: There is no single essential criterion. Despite his overall genius, Karl Jaspers' search for a single pathognomonic feature of delusions was fundamentally misguided. Because his attempt was a fruitful error, eliciting useful thinking and research on the topic, I will briefly review what he tried to do.

Often Jaspers is misinterpreted as suggesting that a certain number of criteria adequately mark out the nature of delusions. The classic criteria are conviction,incorrigibility, and impossibility, derived from the General Psychopathology (Jaspers 1913/1997). But as Walker (1991) has pointed out, Jaspers was only describing those criteria as a starting point, which he considered "superficial." Jaspers wanted to go farther, and identify the essential core of delusions in his criterion of lack of understandability, a radical inability to empathize with or make any sense of a delusional system.

One interpretation is that lack of understandability should be added as a fourth criterion for delusions (with which I agree). But Jaspers himself saw lack of understandability as the essential feature of delusions, and thus he was forced to distinguish delusions (which are un-understandable) from delusion-like ideas (which may meet the other three criteria but not lack of understandability). As Walker notes (1991), this distinction is a weakness of Jaspers' approach, because it would exclude many clinical phenomena that appear to be delusional. Specifically, I think that Jaspers' lack of understandability criterion only picks out bizarre delusions; it leaves nonbizarre delusions untouched. Thus, it is not delusions per se that are identified by lack of understandability, but bizarreness. It is not bizarre to think the FBI is out to get you. Indeed a patient can clearly have a circumscribed paranoid delusion that the FBI is out to get her, and otherwise not have other delusions nor other changes in her behavior, moods, personality, or functioning. We want to say this patient has a delusion. Jaspers' criterion does not capture this scenario.

Neither does impossibility. It is not metaphysically impossible that the FBI is out to get you (or me for that matter). Thus, of Jaspers' four criteria, the circumscribed FBI delusion (especially in the era of the Patriot Act) would only meet the criteria (perhaps) of incorrigibility and conviction. Is that enough to identify it as a delusion? Well, it depends. How many criteria are needed?¹ That would seem to be the right question. But is this a conceptual or an empirical question? If the latter, then we would need some other criterion (such as the consensus of clinicians) on which to base any empirical validation. So it would seem we are back to the conceptual problem.

There is, I think, an underlying assumption here that vexes this issue: the assumption of essentialism. There simply is no essential feature of delusions. We need to be clear about this fact, accept it deep in our souls, live with it, and go on from there in our work. This is, in my adaptation of Daniel Dennett's (1995) phrase, "Darwin's dangerous method." Darwin's key innovation was in realizing that species are not essentialistic; there is no single aspect of the nature of species that necessarily and sufficiently characterizes them. Once this belief was dropped, then the implication that species are unchanging also fell away, and the idea of evolution of species could be born. The biology of species, then, is not essentialistic. I suggest that many notions in biology and medicine (including psychiatry) are not essentialistic. Peter Zachar (2001) has shown, forcefully in my judgment, that psychiatric diagnoses should not be conceived as natural kinds with essential features, but rather as pragmatic kinds. There are those who fear that if we give up the idea of essentialist natural kinds, we will need to give up on real entities, and up rises the specter of postmodernism. Such fear is unfounded, unless one wants...