While the Latin term itself originates in scholasticism, it reflects the Aristotelian view of man as a creature distinguished by a rational principle. In the Nicomachean Ethics I.13, Aristotle states that the human being has a rational principle, on top of the nutritive life shared with plants, and the instinctual life shared with other animals, i. e., the ability to carry out rationally formulated projects. That capacity for deliberative imagination was equally singled out as man's defining feature in De anima III.11. While seen by Aristotle as a universal human feature, the definition applied to wise and foolish alike, and did not in any way imply necessarily the making of rational choices, as opposed to the ability to make them. The Neoplatonic philosopher Porphyry defined man as a "mortal rational animal", and also considered animals to have a rationality of their own. The definition of man as a rational animal was common in scholastical philosophy. Catholic Encyclopedia states that this definition means that "in the system of classification and definition shown in the Arbor Porphyriana, man is a substance, corporeal, living, sentient, and rational". In Meditation II of Meditations on First Philosophy, Descartes arrives at his famous "I think, I exist" claim. He then goes on to wonder "What am I?" He considers and rejects the scholastic concept of the "rational animal":
Shall I say 'a rational animal'? No; for then I should have to inquire what an animal is, what rationality is, and in this one question would lead me down the slope to other harder ones.
Modern use
was as aware as any of the irrational forces at work in humankind, but he nevertheless resisted what he called too much “stress on the weakness of the ego in relation to the id and of our rational elements in the face of the daemonic forces within us”. Neo-Kantian philosopherErnst Cassirer, in his work An Essay on Man, altered Aristotle definition to label man as a symbolic animal. This definition has been influential in the field of philosophical anthropology, where it has been reprised by Gilbert Durand, and has been echoed in the naturalistdescription of man as the compulsive communicator. Sociologists in the tradition of Max Weber distinguish rational behavior from irrational, emotional or confused behavior, as well as from traditional-oriented behavior, but recognise the wide role of all the latter types in human life. Ethnomethodology sees rational human behavior as representing perhaps 1/10 of the human condition, dependent on the 9/10ths of background assumptions which provide the frame for means-end decision making. Bertrand Russell satirized the concept that man is rational, saying "Man is a rational animal — so at least I have been told. Throughout a long life I have looked diligently for evidence in favour of this statement, but so far I have not had the good fortune to come across it." The humor of his observation derives from an equivocation between describing mankind as rational and describing an individual person as rational.
