The main thing that is involved in critical thinking is simply this:  the sustained search for reasons for and against a given claim.

     But we need to consider what this involves.  What I want to suggest is that critical thinking involves three main aspects:

(1) The critical reflex;

(2)  Detailed information about the area under consideration;

(3)  Techniques of critical thinking.

1.  The Critical Reflex.

Illustration:  Aristotle's belief about the relation between the weight of a body, and the speed with which it falls.

     This illustrates rather dramatically the relative rareness of the critical reflex, since we have here a belief that was accepted by the best educated and most intelligent people wherever physics was studied, until the time of Galileo (1564-1642), over 1800 years after the death of Aristotle (384-322 B.C.). And yet it is a belief that a young child can put to the test, and show to be false.

     The rareness of the critical reflex calls to mind Mark Twain's claim, concerning the human species:
 

"It is because they do not think at all; they only think they think.  Whereas they can't think; not two human beings in ten thousand have anything to think with."  (Letters from the Earth, (Greenwich: Connecticut: Fawcett Publications, Inc., 1962), page 19)

     Two in ten thousand does seem, of course, to be an overly pessimistic estimate.  In addition, Twain's remark that most human beings do not have anything to think with tends to suggest that the problem is genetic - though Twain may very well just have been saying, not that most people have defective brains, but that they have minds that have not been properly trained.  In any case, what is crucial here is that possession of the critical reflex is not a matter of any sort of innate intellectual ability: it is simply matter of having acquired skills and habits that anyone can develop.

     The critical reflex, then, is very important, and it can certainly take one a long way.  Nevertheless, it is not always enough on it own, and there are at least two other things that are often very helpful:

2.  Knowledge of the Area under Investigation.

Illustrations:

1.  Scientific American, mediums, and Harry Houdini.

2.  The case of Yuri Geller:

(1)  Yuri Geller and James Randi ("the Amazing Randi" - http://www.randi.org/).

(2)  Spoon bending and a famous British physicist, Professor John G. Taylor: the 'shyness effect'.  (Taylor is professor of mathematics at Kings College, the University of London, and was chosen as one of the world's top twenty scientists in a poll conducted by New Scientist in 1975.)

     Taylor, after being on television with Yuri Geller, and having seen Geller perform, said:  "I felt as if the whole framework with which I viewed the world had suddenly been destroyed.  I seemed very naked and vulnerable, surrounded by a hostile and incomprehensible universe.  It was many days before I was able to come to terms with this sensation."

3.  Critical Thinking Techniques

     There are at least five critical thinking techniques that are very useful when one is considering moral issues:

(1)  Tests for whether arguments are satisfactory in certain ways.  (Exercise on the concept of validity.)

(2) The technique of counterexamples, for evaluating generalizations.  (Exercise on this.)

(3)  The distinction between basic moral claims and derived moral claims.

(4)  The push for general principles that underlie more specific and limited principles.

(5)  The critical evaluation of moral intuitions

Comments

1.  The first two critical thinking techniques are general techniques that one can use with regard to beliefs that fall in any area.

2.  Techniques (3), (4), and (5), by contrast, are specialized techniques that are useful and productive when one is thinking about moral issues.  (We will see that techniques (3) and (4) are especially helpful in areas such as sexual morality, the moral status of non-human animals, and abortion.)