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.

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.