be compos mentis

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

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
References in periodicals archive ?
would Professor "Some of the headshops were only selling to over-18s, and some were only selling to people who appeared to be compos mentis. In my research we found there were some responsible retailers."
I've known people have a single half and feel the effects whereas others could easily drink four or five pints and still be compos mentis. There is no hard and fast rule that x amount of alcohol per 100mg of blood causes the same effects to all.
'They may be compos mentis in a strict legal sense, but people do get more confused as they get older.'