Invitation to Psychology

Chapter 1 What Is Psychology? 15

a hypothesis in such a way that it can be refuted,

or disproved by counterevidence. This principle,

known as the principle of falsifiability, does not

mean that the hypothesis will be disproved, only

that it could be if contrary evidence were to be

discovered.

Another way of saying this is that a scientist

must risk disconfirmation by predicting not only

what will happen, but also what will not happen

if the hypothesis is correct. In the misery-loves-

company study, the hypothesis would be sup-

ported if most anxious people sought each other

out, but disconfirmed if most anxious people

went off alone to sulk and worry, or if anxiety had

no effect on their behavior (see Figure 1.1 on the

next page). A willingness to risk disconfirmation

forces scientists to take negative evidence seri-

ously and to abandon mistaken hypotheses.

The principle of falsifiability is often violated

in everyday life because all of us are vulnerable to

the confirmation bias: the tendency to look for and

accept evidence that supports our pet theories and

assumptions and to ignore or reject evidence that

contradicts our beliefs. Thus, if a police interroga-

tor is convinced of a suspect’s guilt, he or she may

interpret anything the suspect says, even the per-

son’s maintenance of innocence, as confirming evi-

dence that the suspect is guilty (“Of course he says

he’s innocent; he’s a liar”) (Leo, 2008). But what if

the suspect is innocent? The principle of falsifiabil-

ity compels scientists, and the rest of us, to resist the

confirmation bias and to consider counterevidence.

Watch the Video Confirmation Bias

at mypsychlab

5

Avoid Emotional Reasoning. Emotion has a place

in critical thinking and in science. Passionate

commitment to a view motivates people to think

boldly, to defend unpopular ideas, and to seek

evidence for creative new theories. But emotional

conviction alone cannot settle arguments, and in

fact it usually makes them worse. The fact that

you really, really feel strongly that something is

true—or want it to be—doesn’t make it so.

All of us are apt to feel threatened and get

defensive whenever our most cherished beliefs, or

commitment to a course of action, are challenged

by empirical evidence (Tavris & Aronson, 2007).

At such times, it is especially important to separate

the data from emotional reasoning. In our opening

news story about the ruling that vaccines do not

cause autism, one of the judges expressed sympathy

for the parents, but added, “I must decide this case

not on sentiment, but by analyzing the evidence.”

You probably hold strong beliefs about drug

use, the causes of crime, the origins of intel-

ligence, gender differences, obesity, and many

principle of falsifi-

ability The principle that

a scientific theory must

make predictions that are

specific enough to expose

the theory to the possibil-

ity of disconfirmation;

that is, the theory must

predict not only what will

happen but also what will

not happen.

confirmation bias The

tendency to look for or

pay attention only to

information that confirms

one’s own belief, and

ignore, trivialize, or forget

information that discon-

firms that belief.

In scientific research, an idea may initially
generate excitement because it is plausible, imag-
inative, or appealing, but eventually it must be
backed by empirical evidence if it is to be taken
seriously. A collection of anecdotes or an appeal
to authority will not do. Sometimes, of course,
checking the reliability of the evidence directly
is not practical. In those cases, critical thinkers
consider whether it came from a reliable source.
Sources who are reliable exercise critical think-
ing themselves. They usually have education
or experience in the field in which they claim
expertise. They do not pressure people to agree
with them. They share their evidence openly.
They draw on research that has been reviewed
by other experts on the subject, rather than
merely announced to the public in a press release
or blog.

4

Analyze Assumptions and Biases. Assumptions are
beliefs that are taken for granted, and biases are
assumptions that keep us from considering the evi-
dence fairly or that cause us to ignore the evidence
entirely. Critical thinkers try to identify and evalu-
ate the unspoken assumptions on which claims
and arguments may rest—in the books they read,
the political speeches they hear, and the advertise-
ments that bombard them every day. In science,
some of the greatest scientific advances have been
made by those who dared to doubt widespread as-
sumptions: that the sun revolves around the earth,
that illness can be cured by applying leeches to the
skin, that madness is a sign of demonic possession.
Critical thinkers are willing to analyze and
test not only other people’s assumptions, but also
their own, which is much harder. Researchers
put their own assumptions to the test by stating

When demonstrating “levitation” and other suppos-
edly magical phenomena, illusionists exploit people’s
tendency to trust the evidence of their own eyes even
when such evidence is misleading. Critical thinkers ask
about the nature and reliability of the evidence afor a
phenomenon.