What is Critical Thinking?
(William Graham Sumner — 1906)

[Critical thinking is] . . . the examination and test of propositions of any kind which are offered for acceptance, in order to find out whether they correspond to reality or not. The critical faculty is a product of education and training. It is a mental habit and power. It is a prime condition of human welfare that men and women should be trained in it. It is our only guarantee against delusion, deception, superstition, and misapprehension of ourselves and our earthly circumstances.

Education is good just so far as it produces well-developed critical faculty . . . A teacher of any subject, who insists on accuracy and a rational control of all processes and methods, and who holds everything open to unlimited verification and revision, is cultivating that method as a habit in the pupils. Men educated in it cannot be stampeded . . . They are slow to believe. They can hold things as possible or probable in all degrees, without certainty and without pain. They can wait for evidence and weigh evidence . . . They can resist appeals to their dearest prejudices. Education in the critical faculty is the only education of which it can be truly said that it makes good citizens.


{Sumner, W. G. (1940). Folkways: A Study of the Sociological Importance of Usages, Manners, Customs, Mores, and Morals, New York: Ginn and Co., pp. 632, 633.}