Critical thinking is the process of analyzing available facts, evidence, observations, and arguments to make sound conclusions or informed choices. It involves recognizing underlying assumptions, providing justifications for ideas and actions, evaluating these justifications through comparisons with varying perspectives, and assessing their rationality and potential consequences. The goal of critical thinking is to form a judgment through the application of rational, skeptical, and unbiased analyses and evaluation. In modern times, the use of the phrase critical thinking can be traced to John Dewey, who used the phrase reflective thinking, which depends on the knowledge base of an individual; the excellence of critical thinking in which an individual can engage varies according to it. According to philosopher Richard W. Paul, critical thinking and analysis are competencies that can be learned or trained. The application of critical thinking includes self-directed, self-disciplined, self-monitored, and self-corrective habits of the mind, as critical thinking is not a natural process; it must be induced, and ownership of the process must be taken for successful questioning and reasoning. Critical thinking presupposes a rigorous commitment to overcome egocentrism and sociocentrism, that leads to a mindful command of effective communication and problem solving.

In the classical period (5th c.–4th c. BC) of Ancient Greece, the philosopher Plato (428–347 BC) indicated that the teachings of Socrates (470–399 BC) are the earliest records of what today is called critical thinking. In an early dialogue by Plato,^{[citation needed]} the philosopher Socrates debates several speakers about the ethical matter of the rightness or wrongness of Socrates escaping from prison. Upon consideration, Plato concluded that to escape prison would violate everything he believes to be greater than himself: the laws of Athens and the guiding voice that Socrates claims to hear.

Socrates established the unreliability of Authority and of authority figures to possess knowledge and consequent insight; that for an individual man or woman to lead a good life that is worth living, that person must ask critical questions and possess an interrogative soul, which seeks evidence and then closely examines the available facts, and then follows the implications of the statement under analysis, thereby tracing the implications of thought and action.

As a form of co-operative argumentation, Socratic questioning requires the comparative judgment of facts, which answers then would reveal the person's irrational thinking and lack of verifiable knowledge. Socrates also demonstrated that Authority does not ensure accurate, verifiable knowledge; thus, Socratic questioning analyses beliefs, assumptions, and presumptions, by relying upon evidence and a sound rationale.

In modern times, the phrase critical thinking was coined by Pragmatist philosopher John Dewey in his book How We Think. As a type of intellectualism, the development of critical thinking is a means of critical analysis that applies rationality to develop a critique of the subject matter. According to the Foundation for Critical Thinking, in 1987 the U.S. National Council for Excellence in Critical Thinking defined critical thinking as the "intellectually disciplined process of actively and skillfully conceptualizing, applying, analyzing, synthesizing, or evaluating information gathered from, or generated by, observation, experience, reflection, reasoning, or communication, as a guide to belief and action."

In the term critical thinking, the word critical, (Grk. κριτικός = kritikos = "critic") derives from the word critic and implies a critique; it identifies the intellectual capacity and the means "of judging", "of judgement", "for judging", and of being "able to discern". The intellectual roots of critical thinking are as ancient as its etymology, traceable, ultimately, to the critical reasoning of the Presocractic philosophers, as well as the teaching practice and vision of Socrates 2,500 years ago who discovered by a method of probing questioning that people could not rationally justify their confident claims to knowledge.

According to the Oxford English Dictionary, the exact term “critical thinking” first appeared in 1815, in the British literary journal The Critical Review, referring to critical analysis in the literary context. The meaning of "critical thinking" gradually evolved and expanded to mean a desirable general thinking skill by the end of the 19th century and early 20th century.

Traditionally, critical thinking has been variously defined as follows: