Using Logic and evidence to Persuade 17.2 381
the past week. Therefore, you might argue that because the rates are increas-
ing, the Dow Jones Industrial Average will decrease. In this case, you move
from something that has occurred (rising interest rates) to something that
has not yet occurred (decrease in the Dow). Weather forecasters use the same
method of reasoning when they predict the weather. They base a conclusion
about tomorrow’s weather on what they know about today’s meteorological
conditions.- From effect to cause. A second way to frame a causal argument is to reason
backward, from known effect to unknown cause. You know, for example, that
a major earthquake has occurred (known effect). To explain this event, you
propose that the cause of the earthquake was a shift in a fault line (unknown
cause). You cannot be sure of the cause, but you are certain of the effect.
A candidate for president of the United States might claim that the cause
of current high unemployment (known effect) is mismanagement by the
present administration (unknown cause). The candidate then constructs an
argument to prove that his assertion is accurate. To prove his case, he needs
to have evidence that the present administration mismanaged the economy.
The key to developing strong causal arguments is in the use of evidence
to link something known with something unknown. An understanding of
the appropriate use of evidence can enhance inductive, deductive, and causal
reasoning.
Table 17.1 summarizes the three types of reasoning we have discussed.
These logical, rational methods of reasoning, most of which evolved from clas-
sical Greek and Roman traditions of argument, are understood and expected by
most North American audiences. As we’ll see next, however, not all listeners
rely on the same methods.
aDaptIng reasonIng For a Culturally DIverse auDIenCe If a
good portion of your audience has a cultural background that is different from
your own, it’s wise not to assume that they will have the same assumptions
about what is logical and reasonable that you have.
Rhetoricians from the United States typically use a straightforward, factual-
inductive method of supporting ideas and reaching conclusions.^9 They identify
facts and link them to support a specific proposition or conclusion. For example,
in a speech to prove that the government spends more money than it receives, a
speaker could cite year-by-year statistics on income and expenditures to docu-
ment the point. Not all cultures assume such a linear methodical approach to
supporting ideas and proving a point.^10 Some cultures use a deductive pattern
of reasoning rather than an inductive pattern. They begin with a general premise
and then link it to a specific situation when they attempt to persuade listeners.
During several recent trips to Russia, your authors noticed that to argue that
communism was ineffective, many Russians started with a general assumption:
Communism didn’t work. Then they used this assumption to explain specific
current problems in areas such as transportation and education.