Sanity (from Latin: sānitās) refers to the soundness, rationality and healthiness of the human mind, as opposed to insanity. A person is not considered sane anymore just if he/she is irrational. In modern society, the terms have become exclusively synonymous with compos mentis (Latin: compos, having mastery of, and mentis, mind), in contrast with non compos mentis, or insane, meaning troubled conscience. A sane mind is nowadays considered healthy both from its analytical -once called rational- and emotional aspects. Furthermore, according to Chesterton, sanity involves wholeness, whereas insanity implies narrowness and brokenness.
A theory of sanity was proposed by Alfred Korzybski in his general semantics. He believed sanity was tied to the structural fit or lack of thereof, of what is actually going on in the world. He imposed this notion in a map-territory analogy: "A map is not the territory it represents, but, if correct, it has a "similar structure" to the territory, which accounts for its usefulness." Given that science continually seeks to adjust its theories structurally to fit the facts, i.e., adjusts its maps to fit the territory, and thus advances more rapidly than any other field, he believed that the key to understanding sanity would be found in the study of the methods of science (and the study of structure as revealed by science). The adoption of a scientific outlook and attitude of continual adjustment by the individual toward his or her assumptions was the way, so he claimed. In other words, there were "factors of sanity to be found in the physico-mathematical methods of science." And he also stressed that sanity requires the awareness that "whatever you say a thing is, it is not" because anything expressed through language is not the reality it refers to: language is like a map and the map is not the territory. The territory, that is, reality, remains unnamable, un-speakable, mysterious. Hence, the widespread assumption that we can grasp reality through language involves a degree of insanity.