Sanity (from Latin: sānitās) refers to the soundness, rationality, and health of the human mind, as opposed to insanity. A person is sane if they are rational. In modern society, the term has become exclusively synonymous with compos mentis (Latin: compos, lit. 'having mastery of' and Latin: mentis, lit. 'mind'). The contrast is non compos mentis, or insanity. According to the writer G. K. Chesterton,[1] sanity involves wholeness, whereas insanity implies narrowness and brokenness.
A sane mind is nowadays considered healthy both in its analytical (once called rational) and emotional aspects.[2]