The Grammar of Psychiatry
Psychiatrists grade delusions by degree of insight: those with OCD know their obsessions are not true, while those with anorexia may believe their delusions while being aware that others do not share in them; those with schizophrenia believe others share in their delusion. Obsessions (OCD) are distinguished from delusions (schizophrenia) as egodystonic and egosyntonic, respectively.
However psychiatry neglects that obsessions in OCD are in the conditional mood, while delusions in schizophrenia are in the indicative and may be backed up by hallucinations.1
Interestingly, obsessive-compulsive personality disorder (OCPD) is also called anankastic personality disorder; the anankastic conditional in grammar is a sentence of the form “if you want X, you must do Y.” Presumably this grammatical perspective was once known to psychiatrists. Vitousek and Hollon rediscover this among anorexics as the “New Year’s resolution cognitive style”2
If there is a distinctive cognitive style to the eating disorders equivalent to the depressive … bias in memory for negative events…, it is hypothesized to take the form of the New Year's resolution: “I must just do X, so that Y will come to pass—and I shall be the better person for my efforts.”
McHale, V. E. 2021 “The Logic of Schizophrenia” http://vmchale.com/static/serve/schizophrenia.pdf
Vitousek, K. B., & Hollon, S. D. (1990). The investigation of schematic content and processing in eating disorders. Cognitive Therapy and Research, 14 (2), 191–214. https://doi.org/10.1007/BF01176209