Inductive Reasoning: Reaching Conclusions From Evidence • 369example suffers from a lack of representativeness because it does not consider
crows from other parts of the country. If there are rare blue crows in California,
then the conclusion is not true.- Number of observations: The argument about the crows is made stronger by adding
the Washington, DC, observations to the Pittsburgh observations. Adding more obser-
vations would strengthen it further. The conclusion about the sun rising in Tucson is
extremely strong because it is supported by a very large number of observations. - Quality of the evidence: Stronger evidence results in stronger conclusions. For
example, although the conclusion “The sun will rise in Tucson” is extremely strong
because of the number of observations, it becomes even stronger when we consider
scientific descriptions of how the earth rotates on its axis and revolves around the
sun. Thus, adding the observation “Scientific measurements of the rotation of the
earth indicate that every time the earth rotates the sun will appear to rise” strength-
ens the conclusion even further.
Although our examples of inductive reasoning have been “academic” in nature,
we often use inductive reasoning in everyday life, usually without even realizing it. For
example, Sarah has observed, from a course she took with Professor X, that he asked
a lot of questions about experimental procedures on his exams. Based on this observa-
tion, Sarah concludes that the exam she is about to take in another of Professor X’s
courses will probably be similar. In another example, Sam has bought merchandise
from mail order company Y before and gotten good service, so he places another order
based on the assumption that he will continue to get good service. Thus, anytime we
make a prediction about what will happen based on our observations about what has
happened in the past, we are using inductive reasoning.
It makes sense that we make predictions and choices based on past experience,
especially when predictions are based on familiar situations such as studying for an
exam or buying merchandise by mail. However, we make so many assumptions about
the world, based on past experience, that we are using inductive reasoning constantly,
often without even realizing it. For example, did you run a stress test on the chair you
are sitting in to be sure it wouldn’t collapse when you sat down? Probably not. You
assumed, based on your past experience with chairs, that it would not collapse. This
kind of inductive reasoning is so automatic that you are not aware that any kind of
“reasoning” is happening at all. Think about how time-consuming it would be if you
had to approach every experience as if you were having it for the fi rst time. Inductive
reasoning provides the mechanism for using past experience to guide present behavior.
When people use past experience to guide present behavior, they often use shortcuts
to help them reach conclusions rapidly. After all, we don’t have the time or energy to stop
and gather every bit of information that we need to be 100 percent certain that every con-
clusion we reach is correct. These shortcuts take the form of heuristics—“rules of thumb”
that are likely to provide the correct answer to a problem, but are not foolproof.
Using heuristics may sound familiar because we saw in Chapter 3 that people use
heuristics to help them understand what they are seeing (see page 62). Similarly, people
use a number of heuristics in reasoning that often lead to the correct conclusion, but
sometimes do not. We will now describe two of these heuristics, the availability heuris-
tic and the representative heuristic.THE AVAILABILITY HEURISTIC
The following demonstration introduces the availability heuristic.Answer the following questions.- Which are more prevalent in English, words that begin with the letter r or words in which r
is the third letter?
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