be compos mentis

be compos mentis

Sane or mentally competent. The phrase is Latin for "of sound mind." I doubt that Travis was compos mentis when he committed that crime.
See also: compo

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
References in periodicals archive ?
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.
They may be compos mentis in a strict legal sense, but people do get more confused as they get older.