Constructing a Logical Argument:

3. Constructing a Logical Argument: Persuasive Logic. A logical argument aiming to
„prove‟ a point to another person‟s satisfaction will contain a number of premises and
a conclusion.

Arguments can be represented in one of two ways: deductively or inductively.
 Deductive Argument: an argument that purportedly guarantees the truth of the
conclusion, if the premises are true. In other words, a deductive argument is
intended to be constructed in such a way that if all the premises are true, then it is
impossible for the conclusion to be false.
 Inductive Argument: an argument that purportedly makes the truth of the
conclusion highly likely or probable, if the premises are true. In other words, an
inductive argument is intended to be constructed in such a way that if all the
premises are true, then the conclusion is highly likely to be true as well.
You will have to make sure that:
 Your premises or assumptions are valid; and
 Your conclusion actually follows or can be deduced from them.
For example, the following thought processes may sound plausible, but are false:
„Nobody can do two things at once [premise], so you will have to give up one of your
activities [conclusion]‟ – this premise is invalid, for its truth depends on the nature of
activities involved, as well as on one‟s individual capabilities.
„You listen to music while you work [premise] and you have been getting bad results
[premise]: obviously your results are poor because you listen to music! [conclusion]‟
(Not necessarily: there may be a whole lot of other reasons for bad results:
‘x and also y’ does not mean ‘x caused by y’)
„Jane likes John. John is a salesman. Jane must like salesmen [conclusion]. (No – all this
means is that she likes one salesman called John, for reasons that may have nothing to do
with his being a salesman. This is a common error in communication: assumption that
personal reactions are necessarily caused by partiality, bias or prejudice – „because I am a
woman,‟ „because I am foreign,‟ etc.)

„It must be okay [conclusion] because, after all, 6 million people can‟t be wrong
[premise].‟ (Yes they can…)
Apart from the logic of how you have derived your conclusions, there are other factors
affecting the effectiveness of your argument (= eliciting positive response to persuasion).
4. Message Characteristics: Persuasive Style. In this section we will consider a
variety of ways in which we can use message characteristics to influence others. Here
is a sampler of some useful message strategies for effective persuasion:
 Revealing Persuasive Intent. When receivers believe that a source is trying to
change them, they frequently respond defensively. Sources who “forewarn” of
their intent to persuade often put themselves at a major disadvantage precisely
because of the maxim, “Forewarned is forearmed.”
As a general rule, persuasion is more effective when the
forewarning is minimized.
 Organization. Well-organized messages tend to be more persuasive than
disorganized messages. The value of message organization is obvious. If your
message is incoherent and confusing, then receivers will have difficulty merely
understanding. The source may have good arguments, but the receivers will not
comprehend them. (For example, most teachers have had the experience of
presenting information to students in a way that was less than well organized. We
know what happens: the students get confused. They get worried and anxious
because they do not understand. This leads to frustration and creates more barriers
to communication).
 Message Sidedness. There are two sides on every issue. One sided messages
discuss only one perspective. Two sided messages present information on both
sides. Now, one and two sided messages still advocate only one position. The one
sided message ardently defends a position and makes no mention of competing
views. The two sided message also defends a position, but it also “considers” the
other side.
Generally speaking, a two sided message is more
persuasive than a one sided message. To be most effective,
a two sided message must do two things:
 Defend one side;
 Attack the other side.
When two sided messages merely mention that there are
competing perspectives and there is no attack on the
competition, two sided messages are no more effective than
one sided messages. The question is, why are two sided
messages better?
First, two sided messages may simply appear to be more fair and balanced. Thus,
for receivers who are not thinking very carefully, two sided messages make
sources more credible.
Second, for receivers who are thinking carefully, the combination of defense and
attack makes them think even more systematically about the issue and to start

questioning the validity of the “other” side. Thus, two sided messages can provide
a double-barreled strategy where the source gets more support because receivers
like one side and dislike the other.