Definition of Critical Thinking

Critical thinking means correct thinking in the pursuit of relevant and reliable knowledge about the world. Another way to describe it is reasonable, reflective, responsible, and skillful thinking that is focused on deciding what to believe or do. A person who thinks critically can ask appropriate questions, gather relevant information, efficiently and creatively sort through this information, reason logically from this information, and come to reliable and trustworthy conclusions about the world that enable one to live and act successfully in it. Critical thinking is not being able to process information well enough to know to stop for red lights or whether you received the correct change at the supermarket. Such low-order thinking, critical and useful though it may be, is sufficient only for personal survival; most individuals master this. True critical thinking is higher-order thinking, enabling a person to, for example, responsibly judge between political candidates, serve on a murder trial jury, evaluate society's need for nuclear power plants, and assess the consequences of global warming. Critical thinking enables an individual to be a responsible citizen who contributes to society, and not be merely a consumer of society's distractions.
Children are not born with the power to think critically, nor do they develop this ability naturally beyond survival-level thinking. Critical thinking is a learned ability that must be taught. Most individuals never learn it. Critical thinking cannot be taught reliably to students by peers or by most parents. Trained and knowledgable instructors are necessary to impart the proper information and skills. Math and science instructors have precisely this information and these skills. Why?
Critical thinking can be described as the scientific method applied by ordinary people to the ordinary world. This is true because critical thinking mimics the well-known method of scientific investigation: a question is identified, an hypothesis formulated, relevant data sought and gathered, the hypothesis is logically tested and evaluated, and reliable conclusions are drawn from the result. All of the skills of scientific investigation are matched by critical thinking, which is therefore nothing more than scientific method used in everyday life rather than in specifically scientific disciplines or endeavors. Critical thinking is scientific thinking. Many books and papers describing critical thinking present it's goals and methods as identical or similar to the goals and methods of science. A scientifically-literate person, such as a math or science instructor, has learned to think critically to achieve that level of scientific awareness. But any individual with an advanced degree in any university discipline has almost certainly learned the techniques of critical thinking.
Critical thinking is the ability to think for one's self and reliably and responsibly make those decisions that affect one's life. Critical thinking is also critical inquiry, so such critical thinkers investigate problems, ask questions, pose new answers that challenge the status quo, discover new information that can be used for good or ill, question authorities and traditional beliefs, challenge received dogmas and doctrines, and often end up possessing power in society greater than their numbers. It may be that a workable society or culture can tolerate only a small number of critical thinkers, that learning, internalizing, and practicing scientific and critical thinking is discouraged. Most people are followers of authority: most do not question, are not curious, and do not challenge authority figures who claim special knowledge or insight. Most people, therefore, do not think for themselves, but rely on others to think for them. Most people indulge in wishful, hopeful, and emotional thinking, believing that what they believe is true because they wish it, hope it, or feel it to be true. Most people, therefore, do not think critically.
Critical thinking has many components. Life can be described as a sequence of problems that each individual must solve for one's self. Critical thinking skills are nothing more than problem solving skills that result in reliable knowledge. Humans constantly process information. Critical thinking is the practice of processing this information in the most skillful, accurate, and rigorous manner possible, in such a way that it leads to the most reliable, logical, and trustworthy conclusions, upon which one can make responsible decisions about one's life, behavior, and actions with full knowledge of assumptions and consequences of those decisions.
Raymond S. Nickerson (1987), an authority on critical thinking, characterizes a good critical thinker in terms of knowledge, abilities, attitudes, and habitual ways of behaving. Here are some of the characteristics of such a thinker:
uses evidence skillfully and impartially

organizes thoughts and articulates them concisely and coherently

distinguishers between logically valid and invalid inferences

suspends judgment in the absence of sufficient evidence to support a decision

understands the difference between reasoning and rationalizing

attempts to anticipate the probable consequences of alternative actions

understands the idea of degrees of belief

sees similarities and analogies that are not superficially apparent

can learn independently and has an abiding interest in doing so

applies problem-solving techniques in domains other than those in which learned

can structure informally represented problems in such a way that formal techniques, such as mathematics, can be used to solve them

can strip a verbal argument of irrelevancies and phrase it in its essential terms

habitually questions one's own views and attempts to understand both the assumptions that are critical to those views and the implications of the views

is sensitive to the difference between the validity of a belief and the intensity with which it is held

is aware of the fact that one's understanding is always limited, often much more so than would be apparent to one with a noninquiring attitude

recognizes the fallibility of one's own opinions, the probability of bias in those opinions, and the danger of weighting evidence according to personal preferences
This list is, of course, incomplete, but it serves to indicate the type of thinking and approach to life that critical thinking is supposed to be. 

Similar descriptions of critical thinking attributes are available in the very extensive literature of critical thinking. See, for example, Teaching Thinking Skills, 1987, edited by J. B. Baron and R. J. Steinberg; Developing Minds: A Resource Book for Teaching Thinking, 1985, edited by A. L. Costa; The Teaching of Thinking, 1985, edited by R. S. Nickerson and others;Critical Thinking, Fifth Edition, 1998, by B. N. Moore and Richard Parker, and Critical Thinking, Second edition, 1990, by John Chaffe. These books are representative of the genre.