Scottish psychologist, born in Kirkcudbrightshire, bred to medicine; professor of Moral Philosophy in the University of Edinburgh, colleague and successor to Dugald Stewart; his lectures, all improvised on the spur of the moment, were published posthumously; "Lectures on the Philosophy of the Human Mind" established a sixth sense, which he called the "muscular." He was a man of precocious talent, and a devoted student, to the injury of his health and the shortening of his life; he was obliged from ill-health to resign his professorship after 10 years (1778-1820).