There are many different definitions of critical thinking. Here we list some of the well-known ones. It can be seen that they all emphasize the importance of clarity and rationality. Here we will look at some well-known definitions in chronological order.

Many people traced the importance of critical thinking in education to Dewey. But Dewey did not make very extensive use of the term "critical thinking". Instead, in his book How We Think, he argued for the importance of what he called "reflective thinking":

... [when] the ground or basis for a belief is deliberately sought and its adequacy to support the belief examined. This process is called reflective thought; it alone is truly educative in value ...
Active, persistent and careful consideration of any belief or supposed form of knowledge in light of the grounds that support it, and the further conclusions to which it tends, constitutes reflective thought.

There is however one passage where Dewey explicitly uses the term "critical thinking":

The essence of critical thinking is suspended judgment; and the essence of this suspense is inquiry to determine the nature of the problem before proceeding to attempts at its solution. This, more than any other thing, transforms mere inference into tested inference, suggested conclusions into proof.
Dewey (1910) How We Think, p74.

The Watson-Glaser Critical Thinking Appraisal (1980) is a well-known psychological test of critical thinking ability. The authors of this test define critical thinking as :

... a composite of attitudes, knowledge and skills. This composite includes: (1) attitudes of inquiry that involve an ability to recognize the existence of problems and an acceptance of the general need for evidence in support of what is asserted to be true; (2) knowledge of the nature of valid inferences, abstractions, and generalizations in which the weight or accuracy of different kinds of evidence are logically determined; and (3) skills in employing and applying the above attitudes and knowledge.

A very well-known and influential definition of critical thinking is from Robert Ennis (1987):

Critical thinking is reasonable reflective thinking that is focused on deciding what to believe or do.
Ennis (1987) A taxonomy of critical thinking dispositions and abilities. In Baron and Sternberg (Eds.) Teaching thinking skills: Theory and practice. NY: W.H. Freeman, pp. 9-26.

This definition comes from a statement written in 1987 by Michael Scriven and Richard Paul, National Council for Excellence in Critical Thinking, an organization promoting critical thinking in the US.

Critical thinking is the intellectually disciplined process of actively and skillfully conceptualizing, applying, analyzing, synthesizing, and/or evaluating information gathered from, or generated by, observation, experience, reflection, reasoning, or communication, as a guide to belief and action. In its exemplary form, it is based on universal intellectual values that transcend subject matter divisions: clarity, accuracy, precision, consistency, relevance, sound evidence, good reasons, depth, breadth, and fairness. It entails the examination of those structures or elements of thought implicit in all reasoning: purpose, problem, or question-at-issue, assumptions, concepts, empirical grounding; reasoning leading to conclusions, implications and consequences, objections from alternative viewpoints, and frame of reference.

The following excerpt comes from Peter A. Facione (1990) "Critical Thinking: A Statement of Expert Consensus for Purposes of Educational Assessment and Instruction", a report for the American Philosophical Association.

"We understand critical thinking to be purposeful, self-regulatory judgment which results in interpretation, analysis, evaluation, and inference, as well as explanation of the evidential, conceptual, methodological, criteriological, or contextual considerations upon which that judgment is based. CT is essential as a tool of inquiry. As such, CT is a liberating force in education and a powerful resource in one's personal and civic life. While not synonymous with good thinking, CT is a pervasive and self-rectifying human phenomenon. The ideal critical thinker is habitually inquisitive, well-informed, trustful of reason, open-minded, flexible, fairminded in evaluation, honest in facing personal biases, prudent in making judgments, willing to reconsider, clear about issues, orderly in complex matters, diligent in seeking relevant information, reasonable in the selection of criteria, focused in inquiry, and persistent in seeking results which are as precise as the subject and the circumstances of inquiry permit. Thus, educating good critical thinkers means working toward this ideal. It combines developing CT skills with nurturing those dispositions which consistently yield useful insights and which are the basis of a rational and democratic society."

If you are interested in some further discussion about the definition of critical thinking, you can read this sample chapter from Alec Fisher's book on critical thinking here:

Here are some other people trying to explain critical thinking. Evaluate their claims in light of what you have read above.

  1. In this Wall Street Journal article, someone defined critical thinking as "forming your own opinion from a variety of different sources."
  2. "Actually, the essence of critical thinking lies in asking questions and to keep asking them until you are satisfied with the answer." Ho Lok-sang, Director of the Centre for Public Policy Studies at Lingnan University. China Daily, Tuesday, December 30, 2014