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Supporting Materials 291

reasoning from Specific instances and generalizations
When reasoning from specific instances (or examples), you examine
several specific instances and then conclude something about the whole.
This form of reasoning, known as induction, is useful when you want to
develop a general principle or conclusion but cannot examine the whole.
For example, you sample a few communication courses and conclude
something about communication courses in general; you visit several
Scandinavian cities and conclude something about the whole of Scandi-
navia. In reasoning from specific instances, be sure to examine a suffi-
cient number of instances. Three general guidelines will help you deter-
mine how much is enough.
● The larger the group you want your conclusion to cover, the greater
the number of specific instances you should examine. If you wish to
draw conclusions about members of an entire country or culture,
you’ll have to examine a considerable number of people before draw-
ing even tentative conclusions.
● The greater the diversity of items in the class, the more specific in-
stances you will have to examine. Pieces of pasta in boiling water are “In the Interest of streamlining the judicial process, we’ll
all about the same; thus, sampling one usually tells you something skip the evidence and go directly to sentncing.”
about all the others. On the other hand, college courses are probably @ J.B. Handelsman/Condé Nast Publications/www.cartoonbank.com
very different from one another, so valid conclusions about the entire
range of college courses will require a much larger sample.
● Beware of anecdotal evidence. Often you’ll hear people use anecdotes to “prove” a point:
“Women are like that; I have three sisters.” “That’s the way Japanese managers are; I’ve
seen plenty of them.” One reason this type of “evidence” is inadequate is that it over-
generalizes on the basis of too few observations. A second reason is that one person’s
observations may be unduly clouded by his or her own attitudes and beliefs.

reasoning from Causes and effects When reasoning from causes and effects, you
may go in either of two directions: (1) You may reason from cause to effect—for example,
Smoking (the cause) contributes to lung cancer (the effect)—or (2) you may reason from effect
to cause: for example, Low reading scores among elementary school children (the effect) are
due to poverty (the cause). In order to establish a cause-effect connection, you need to prove
that possible causes other than the one you’re postulating are not producing the effect. And
so you’d need to determine whether causes other than smoking may contribute to lung can-
cer, or whether factors other than poverty contribute to low reading scores. Usually you
won’t be able to rule out all other factors, but it’s important to demonstrate that the factors
you are identifying are the main contributors. Scientific studies on the effects of smoking on
cancer rates and the effects of poverty on reading scores would enable you to establish these
cause-effect relationships.
You’d also want to demonstrate that the causation is in the direction you say it is. If two things
occur together, it’s often difficult to determine which is the cause and which is the effect. For exam-
ple, a lack of interpersonal intimacy and a lack of self-confidence often occur in the same person
but it’s not clear which is the cause and which is the effect or even if a causal relationship exists.

reasoning from Sign When reasoning from sign, you may draw a conclusion on the
basis of the presence of clues or symptoms that frequently occur together. Medical diagno-
sis is a good example of reasoning by sign. The general procedure is simple: If a sign and
an object, event, or condition are frequently paired, the presence of the sign is taken as
proof of the presence of the object, event, or condition. For example, fatigue, extreme
thirst, and overeating serve as signs of hyperthyroidism, because they frequently accom-
pany the condition.
You’d also want to show that other signs cannot logically point to the same conclusion.
In the thyroid example, extreme thirst could be brought on by any number of factors. Simi-
larly, the fatigue and the overeating could be attributed to other causes. Yet, taken together,