What is Critical Thinking? Most of us would agree that critical thinking is the mental process on the basis of which we make reliable judgements on the credibility of a claim or the desirability of a course of action. Members of a jury use their critical faculty to scrutinize the evidence presented in court to decide whether the accused is guilty or innocent. Members of a board of directors use their critical faculty to decide whether a proposed reform would be beneficial or harmful.

The above characterization of critical thinking contrasts with the narrow view that equates critical thinking with the application of classical deductive and inductive logic, and the use of the checklist of the logical fallacies found in logic textbooks. Pedagogical approaches that incorporate the logic-based view have two serious flaws. First, they give the misleading impression that reasoning is the sole ingredient of critical thinking. Other central ingredients of critical thinking, such as assessing the credibility of the facts presented, looking for additional facts which could be inconsistent with the proposed conclusion, looking for alternative conclusions, choosing between alternative conclusions, and so on, hardly ever figure in traditional treatments.

Second, even within reasoning, the traditional programme ignores the types of formal and informal reasoning that lie outside the domain of classical logic. Traditional logic covers only a small fragment of the reasoning actually used in academic activities and everyday life. For instance, most traditional books on critical thinking hardly mention the central concepts of critical thinking needed for the assessment of conclusions based on experimentation, such as sampling biases and standard deviation, as such topics are found in textbooks on statistics rather than classical logic.

Given the above view, let us ask: Can critical thinking be taught? The answer depends on what we mean by "teaching'. If "teach x critical thinking" means "make x think critically", the answer is probably no. But if it means "help x acquire the ability to think critically" or "help x improve the ability to think critically", the answer is yes. If teachers can help their students learn to paint, sing, dance or play chess, they can also help students develop or improve the ability to think critically.

How can we teachers help our students develop their critical thinking faculty? A standard response would be: give the students one or two lectures on critical thinking. However, I doubt very much if we can make any serious difference if a curriculum devotes to critical thinking one or two lectures, or even a whole module, but ignores it in remaining modules. Whether or not such specialized lectures or modules are available, we need to incorporate critical thinking in every module we teach.

Viewed from the broad perspective of the modes of assessing the credibility of claims and the desirability of actions, we may distinguish between global and discipline-bound critical abilities. When I critically read a research paper in my area of specialization and make an assessment of the claims made in the paper, I use my discipline-bound critical faculty, which involve making use of the information, available in my discipline, as well as the modes of thinking frequently employed in my discipline. In contrast, when I critically read a newspaper article on an article in Scientific American on a topic outside my discipline I use my global critical faculty These two levels of critical think ing clearly interact and reinforce each other.

From this vantage point, each module taught in a university has a role to play in strengthening certain aspects of critical thinking. For instance, a module in experimental psychology may tend to focus on the ability to assess experiment design and statistical data, while a module in theoretical chemistry may tend to focus on the ability to assess theoretical interpretations, test predictions, look for alternative interpretations, and so on. Hopefully, the combined effort from a number of disciplines will lead to the enhancement of global critical thinking as well.

A frequently-voiced complaint among university teachers is that students are unwilling, or even unable, to think critically. Assuming that this feeling is not baseless, let us ask: Why is critical thinking underdeveloped among students? The answer, I think, can be stated as follows. An essential prerequisite for the development of critical thinking among students is the critical understanding of what they learn in their classes. The traditional framework of education that most of us rely on does not have a provision for critical understanding, and hence does not facilitate critical thinking.

By critical understanding I mean the understanding that involves not only familiarity with the concepts and propositions that we call knowledge, and the ability to apply them to new situations, but also an awareness and appreciation of the evidence for what is presented as knowledge. Textbooks and lectures typically present the conclusions arrived at by the academic community, but they rarely present the evidence that leads to these conclusions, or the arguments that support them. In the absence of evidence and argumentation, students are not in a position to critically evaluate the knowledge presented to them. All they can do is accept on trust what is handed down to them, a situation that is hardly conducive to the practice of critical thinking.

Let me explain. Most educated people in the twentieth century believe that the earth rotates around its axis, and revolves around the sun. However, very few people realize that these are not observable facts, but only theoretical interpretations supported by considerable evidence. The only way to observe the earth's revolution around the sun is to go outside the solar system, for which space travel has not equipped us with yet. There is no way to observe the earth's rotation, unless we go outside the universe to observe the earth and the stars from an independent reference point. When viewed from the earth, all we can see is a pattern of changes in the location of the heavenly bodies: while the position of the star called Polaris appears fixed, the rest of the stars describe a circular motion around Polaris. This observed fact can in principle be explained by assuming either that the earth rotates around its axis, or that the sky rotates around the earth. Why then do we now accept the former hypothesis rather than the latter one? The answer is that the assumption of the earth's rotation (combined with a few other assumptions) allows us to calculate, in a simpler manner, the observed changes in the locations of stars and other heavenly bodies. Until we can find a better set of assumptions, we must subscribe to the hypothesis of the earth's rotation.

Critical understanding entails raising the question (e.g., What is the evidence that justifies the assumption of the earth's rotation?) and being able to make an assessment of the evidence. For students to become aware of such questions of evidence and to assess the evidence relevant to conclusions, it is important that textbooks and teachers help them become aware of this dimension of human knowledge. By and large, traditional education does not deal with questions like:

• What is the evidence to assume that human beings evolved from monocellular organisms?
• What is the evidence to assume that oxygen has a valency of two?
• Why should we assume that there are such things as electrons, and that they are negatively charged?
• Why should we assume that there is such a thing as social class?

For instance, chemistry textbooks tell students that a molecule of water consists of two atoms of hydrogen and one atom of oxygen, but they generally do not discuss the facts and arguments that support this conclusion, let alone discuss Dalton's idea that one atom of hydrogen combines with one atom of oxygen. As a result, students get into the habit of uncritically accepting as facts the theoretical assumptions presented to them in their textbooks and lectures. By leaving out critical understanding from the curriculum, the traditional framework of education pre-empts the possibility of critical thinking.

As long as textbooks and lectures fail to deal with evidence, alternative conclusions and argumentation, it would be unrealistic to expect students to develop critical thinking. The first step towards the teaching of critical thinking is therefore bringing into our syllabuses, lectures and examination questions, not only the conclusions accepted in the academic community, but also the evidence and argumentation that demonstrate the credibility or lack of credibility of these conclusions and their alternatives.