be compos mentis

To be sane or mentally competent. "Compos mentis" is Latin for "of sound mind." I doubt that Travis was compos mentis when he committed that crime.
See also: compo, mentis

non compos (mentis)

Not sane or mentally competent. The phrase is Latin for "not of sound mind." Based on the orders he's been giving lately, many believe him to be non compos. The judge ruled that she had been non compos mentis at the time, and thus could not be held legally liable.
See also: compo, non
Farlex Dictionary of Idioms. © 2022 Farlex, Inc, all rights reserved.

be ˌcompos ˈmentis

(from Latin, formal or humorous) having full control of your mind: Are you sure she was fully compos mentis when she said that?
See also: compo, mentis
Farlex Partner Idioms Dictionary © Farlex 2017
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References in periodicals archive ?
1932), Speculum Mentis (1924), The Archaeology of Roman Britain (1930), An Essay on Philosophical Method (1933), The Principles of Art (1938), The New Leviathan (1942), The Idea of History (1946, posthumous)
Thomas Aquinas, and he is best known for Itinerarium mentis ad Deum (tr The Mind's Road to God, 1953).
We do our fogey chat when we see each other, both loners, a state forced on us by fate rather than choice, because we know that interaction with fellow human beings is a vital part of keeping ourselves compos mentis rather than compost mentis, as he likes to tell me with a chuckle.
M2 EQUITYBITES-October 27, 2017-Civitas Completes Acquisition of Mentis Neuro Rehabilitation
Chief customer officer, Business and Private Banking, Angela Mentis, said, 'Australia's future economic prosperity is inextricably linked to fast growth sectors like Agribusiness, Health and Education.
Called to the hospital midafternoon, I had mixed feelings, partly hoping for frankly unexpected positive news, and partly hoping that if compos mentis, she would overlook my missing the match for a mere hospital visit.
New York, NY, September 21, 2016 --( MENTIS Software, the long-time leader in the sensitive data protection market, today announced the launch of its newly revamped website.
"When I'm out talking to business owners across the country they tell me Australia is a great place to live, work and do business," said Angela Mentis, NAB Group Executive Business Banking.
US-based real estate investor Capital Square Realty Advisors, LLC has acquired a newly-constructed 19,855-square-foot medical rehabilitation facility in El Paso, Texas, that is 100% leased to Mentis Neuro El Paso LLC, the company said.
"She was still compus mentis. She wasn't confused, she had all her wits about her.
Once I was compos mentis, I was humbled by the kindness shown by my friends and colleagues in the office towards me in my hour of need.