When Did Neurosis and Psychosis Swap Meanings?

Andrew Scull says neurosis and psychosis crossed over sometime in the late nineteenth century. Before that crossover, neurosis meant a disorder rooted in the brain, which shows in the root of the word, and psychosis meant a disorder that came from the mind, the psyche.

In the twentieth and twenty-first centuries the names in use are neuroses, neurotic diseases, and psychotic diseases. Present usage separates out the core, the most severe forms of mental disorder. The severe forms include Alzheimer's disease and other forms of dementia, very serious depression, and bipolar disorder, where people oscillate into extreme mania. In extreme mania they get no sleep, talk at an extraordinary rate, behave in ways that are very hard to tolerate, exhaust themselves, and may even die from exhaustion if the mania is not controlled.

The nineteenth-century split sorted mental disorder by whether the trouble was rooted in the brain or came from the mind. After the late nineteenth century the two terms crossed over, and present talk gathers Alzheimer's disease, other dementias, very serious depression, and bipolar mania as the core severe disorders.