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Critical Thinking

Psychologists as a group tend to be skeptical. In other words, they have a "show me" or "prove it to me" attitude. Most encourage their students to practice critical thinking.

Critical thinking does not neces­sarily mean making criticisms. It means doing a good job of evaluating evidence. It means developing intellectual tools to avoid being gullible or easily taken in by false claims or "quack" science (highly questionable or absurd ideas presented as though they are scientific truths).

What is reportedly true of psychologists as a group?

The phrase critical thinking became popular among educators in the 1950s, but in 1998 psychologist Diane Halpern said critical thinking was "more important than ever" for today's students (Halpern, 1998). The rising tide of inaccurate information online in the early decades of the 21st Century only reinforces her point.

Video platforms like YouTube do not discriminate between fact and fiction. For every useful docu­mentary about a psychology-related topic, there are hundreds pseudo-documentaries about conspiracies, UFOs, hidden planets threatening the earth, and much more. Students need critical thinking to separate the wheat from the chaff (separate what is valuable from what is useless).

Critical thinking has been described in many ways over the years, but there are some recurrent themes:

Avoid jumping to conclu­sions [Suspend judgment; keep an open mind until you have adequate evidence; tolerate uncertainty; avoid oversimpli­fication.]

Examine assumptions [Identify premises or starting assump­tions; avoid accepting an idea simply because it appeals to pre-existing biases or assumptions.]

Generate new ideas [Experiment with ideas opposite to those normally considered; ask questions; consider other perspectives.]

Evaluate evidence [Ask whether an idea generates surprising predictions. Look for actual tests of an idea. See what experts in the field have to say about controversial ideas.

This is good advice. None of it is new. Some of it is antique. William James wrote in 1876 that "philosophic study means the habit of always seeing an alternative" (James, 1876/1978). The Greeks made similar statements.

What are recurrent themes in discussions of "critical thinking"?

The fourth theme is perhaps the most important. At the end of the day, after staying open-minded and generating new ideas, one is left with the problem of evaluating evidence

This is the specialty of science: gathering and evaluating evidence. Knowledge about this process is a major weak spot in public education in the U.S. and probably in other countries as well.

When the National Science Foundation in the United States surveyed public attitudes and knowledge about science, they found that 70% of American adults said they were "interested" in science. However, fewer than 30% could give a passable definition of a scientific experiment or hypothesis. Rensberger (2000) wrote:

Without a grasp of the scientific ways of thinking, the average person cannot tell the difference between science based on real data and something that resem­bles science–at least in their eyes–but is based on uncontrolled experiments, anec­dotal evidence, and passionate assertions. They like it all.

The claim, for example, that brains can transmit information telepathically, strikes them as no less believable than the claim that whole stars can collapse into infinitesimal points. Many among the public have not yet learned that what makes science special is that evidence has to meet certain standards.

All the critical thinking instruction in the world will not help people distinguish between true and false claims if they do not have a grasp of what constitutes scientific evidence. We will discuss some basic principles in this course. However, to gain a deeper understanding of science, the best method is to take several courses in natural sciences at a good college or university.

What is the "weak spot" in education for critical thinking?

For somebody without higher education, how can one explain the nature of scientific evidence? It is easy (but perhaps not very effective) to give an abstract description.

To gather evidence about a theory or model: (1) Use it to generate risky predictions. (2) Test them. (3) If the predictions fail, give up or adjust the model and try again. (4) If surprising predictions come true, replicate them. (5) Cumulate and integrate such findings.

Unfortunately, this does not help somebody who knows little about science. If they cannot evaluate evidence themselves, they must rely upon authority.

But what sources are trustworthy? The journals Science and Nature? The BBC for news?

What is a sketchy and abstract summary of how evidence is gathered? For people who cannot do this themselves, what is the alternative?

Wikipedia, the most-cited information source on the internet, is not a bad place to look for unbiased knowledge. People criticize it, but Wikipedia does a good job, especially given the universal scope of its coverage.

Wikipedia demands references, and it refuses to describe a theory as credible unless there is evidence for it. That is an important filter, similar to science in general. Wikipedia also encourages correction of errors.

To go beyond locating trustworthy authorities, to actually achieve scientific literacy as a student, there is perhaps no substitute for a college or university education. After taking a few courses in the natural sciences, a student may notice that they have a lot in common.

A student who takes two or more science courses also discovers they are mutually consistent. Nothing encountered in biology class should contradict geology class, psychology class, astronomy, botany, genetics, anthropology, or any other evidence-based science.

The underlying reason for this consistency is that all scientific theories are tested against the same external universe. There is only one reality "out there."

All the accurate theories or maps of that reality are different views of the same system. If they are true to the data, they will be consistent with each other.

Once a student grasps this truth, science in general becomes more credible. Students realize that a theory, to be accepted, must not only generate risky predictions. It must also mesh with a body of other well-tested, verified theories. Science is not just a claim here or there; it is a vast network of consistent ideas, a map of the universe.

Also important is the fact that scientists seek continually to improve existing theories. A researcher who corrects an error is rewarded. Career advancement depends upon contributing to the cumulative body of knowledge, not confirming existing theories.

That does not mean individual scientists cannot be wrong. Scientists are human. Some are stubborn. But science is an institution spanning many countries, involving many thousands of people. Controversies occur, but eventually the ideas supported by good evidence rise to the top.


Halpern, D. F. (1998) Teaching critical thinking for transfer across domains. American Psychologist, 53, 449-455.

James, W. (1876/1978) The teaching of philosophy in our colleges. In: James, W., Burkhardt, F., Bowers, F., & Skrupskelis, I. K. (1876/1978) Essays in philosophy. Cambridge, MA: Harvard University Press.

Rensberger, B. (2000) Why scientists should cooperate with journalists. Science and Engineering Ethics, 6, 549-552. doi:10.1007/s11948-000-0014-2

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