Examples
My history professor said everyone who
wrote a term paper favoring the sepa-
ratists in the Philippines is sick. I guess if
I’m sick, I can skip class today.
The word “sick” is used in the argument
twice, each with a different meaning. The
professor meant mentally disturbed, and
the student thought he meant physically
ill.
Hot dogs are better than nothing. Noth-
ing is better than steak. Therefore, hot
dogs are better than steak.
It is not hard to spot the logical fallacy in this
argument: the conclusion is obviously wrong although
the premises are both true. There is an equivocation in
the meaning of the word “nothing;” in the first prem-
ise, it means “not a thing,” and in the second premise,
it means “no other possible thing.” Using a critical word
with two different meanings makes the argument
invalid.
Now you see how one word with two different
meanings can be an equivocation. The other way in
which reasoning may be deemed invalid due to this fal-
lacy is by using one word that has a number of differ-
ent meanings. For example, “My house is by the lake.
Why don’t you drop in?” Two meanings of the word
“drop” could be right. It might mean, “Why don’t you
stop by my house,” or it could mean “why don’t you fall
into the lake.” The equivocation of the word “drop”
makes the meaning of the sentences unclear.“Save soap
and waste paper” is another good example. The word
“waste” could mean either the noun “garbage,” or the
verb “to use thoughtlessly.”
Equivocation can be confusing because it begins
with truthful or reasonable premises, which you can
agree with. Then, the meaning of a critical word is
changed and an illogical or faulty conclusion is drawn.
If you follow the argument, you could fall into the trap
of agreeing with something you would never have oth-
erwise accepted. The best way to handle this fallacy is
to get information. Ask for clear definitions of any crit-
ical terms that could be used in different ways. When
you have pinned them down, they can’t be changed
later on.
Practice
Which word in each example is the equivocation?
1. The sign said “fine for parking here”, and since it
was fine, I parked there.
2. The IRS allows a deduction for every dependent
in a household. My dog is dependent on me, so I
can claim a deduction for him.
3. If all men are created equal, then why are
geniuses so smart?
4. Everything that runs has feet. The refrigerator
runs, so the refrigerator has feet.
Answers
1. fine
2. dependent
3. equal
4. runs
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In Short
Not all deductive reasoning is reasonable. It may be
flawed factually, meaning all or part of it is untrue. Or,
it may be flawed logically, and contain a fallacy. It is
important to be able to recognize logical fallacies so
they do not persuade or mislead you. Some of the most
common of these fallacies are slippery slope, false
dilemma, circular reasoning, and equivocation.
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■Find a newspaper or magazine article that contains quotes from one or more politicians. Do any
of them use logical fallacies in their arguments? If so, which ones?
■Think of an extravagant purchase you would like to make. Devise two arguments for buying the
item, using both false dilemma and circular reasoning fallacies.
Skill Building Until Next Time
INDUCTION IS THE process of reasoning from the specific (particular facts or instances) to the gen-
eral (principles, theories, rules). It uses two premises that support the probable truth of the conclu-
sion. Thus, an inductive argument looks like this: If A is true and B is true, then C is probably true.
How can you determine or measure what is probable or improbable? By using two things:
1. past experience
2. common sense
Past experience tells you what you might be able to expect. For instance, “for the past three weeks, my
colleague has showed up a half hour late for work. Today, she will probably be late, too.” Common sense
allows you to draw an inference, or a “smart guess,” based on the premises, such as, “They need five people
on the team. I’m one of the strongest of the seven players at the tryouts. It’s likely that I will be picked for
the team.”
LESSON
Inductive
Reasoning
LESSON SUMMARY
This lesson shows how to recognize and construct an inductive argu-
ment. These arguments move from specific facts to general conclu-
sions by using common sense and/or past experience.
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105
Because you must make a leap from the premises
to the truth of the conclusion, inductive reasoning is
more likely to fail and produce fallacies, such as a hasty
conclusion fallacy (see Lesson 15 to learn about these fal-
lacies). Even so, most reasoning is inductive. One of the
basic theories of modern biology, cell theory, is a prod-
uct of inductive reasoning. It states that because every
organism that has been observed is made up of cells, it
is most likely that all living things are made up of cells.
There are two forms of inductive arguments.
Those that compare one thing, event, or idea to another
to see if they are similar are called comparative argu-
ments. Those that try to determine cause from effect
are causal arguments.
Practice
Use possible past experience and common sense to
choose the best conclusion for the inductive argu-
ment that begins: The other thirteen people who
work on my team
a. liked the design of the new product, so I should
too.
b. got positive evaluations from our boss, so I
should too.
c. got sick after eating the tuna salad, so I will too.
d. who met the new employee liked him, so I will
too.
Answer
The answer is c. Based on past experience, we know that
some foods can make people ill due mainly to bacteria
contamination. Common sense tells us that if 13 peo-
ple ate tuna salad and got sick, most everyone else who
ate it will get sick, too.
Comparison Arguments
Inductive arguments arise from experiences or obser-
vations. They compare one event, idea, or thing with
another to establish that they are similar enough to
make a generalization or inference about them. The
most important point to note about this type of argu-
ment is that the two events being compared must be
similar.
Example
Rebekah says, “Whenever I use bread flour
to make my pizza, the crust turns out per-
fectly. So, every time I use bread flour, I
will have a perfect crust.” (A leads to B
many times, so A will lead to B every
time.)
Rebekah is comparing one set of events (observed
use of bread flour and perfect pizza crust) with another
(a generalization: every time she uses bread flour, she
will get a perfect crust). These events have one simi-
larity (using bread flour), and the inductive argument
is that they will also be similar in another way (result
in a perfect pizza crust).
The strength of this, as well as all other, compar-
ative inductive arguments depends on how similar the
two events are. In fact, when an inductive argument
fails, it is most often because the events were not really
similar enough to make a comparison. Rebekah takes
for granted that “every time” in the future, she will
make pizza exactly as she did during each of the
observed times. If that is true, her conclusion is prob-
ably true.
But what if every observed time Rebekah used the
bread flour, she also used fresh yeast? If she makes a
pizza in the future and uses old yeast, she will not get
a perfect crust. The events will be dissimilar and the
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106
conclusion will not hold. The second premise of any
inductive argument should ideally state that there is no
significant difference between the two sets of
events/ideas/things. The second premise of Rebekah’s
argument could say “Every crust will be perfect, because
there will be no key difference between my future crust
making and my previous crust making.” Keeping such
a disclaimer in mind is important, because this is where
many inductive arguments are weakest.
Practice
How could you strongly conclude the following induc-
tive argument?
We have read over one hundred pages of
her poetry manuscript. So far, the poems
about nature are strong and finely crafted,
and those about love and relationships are
loose and even sometimes sloppy. So we
expect in the next hundred pages to
find . . .
Answer
You can conclude that her love poetry is loose and
sometimes sloppy, and her nature poetry is finely
crafted.
Practice
Which is NOT an example of a comparison argument?
a. This month I paid my bills on time and I didn’t
get charged any late fees. Next month I’m going
to pay them on time too so I can avoid the fees.
b. I got so tired at work yesterday afternoon after I
had a bagel for lunch. Tomorrow, I think I’ll
order a roast beef sandwich.
c. Tom works out every morning and so does Bill.
They are both in great shape and have lots of
energy. If I work out every morning, I could get
in shape and have more energy.
d. The chunky peanut butter was 50 cents cheaper
at the supermarket every week for the past
month. This week, it will probably be 50 cents
cheaper, too.
Answer
The answer is choice b. While it might make sense to
order something else other than a bagel to avoid get-
ting tired, this argument does not show any similari-
ties between one event and another. It is really a causal
argument. This type of argument is examined next.
Causal Arguments
The inductive arguments above relied on the estab-
lishment of similarities between two events, ideas, or
things. Causal arguments, which may be used to figure
out the probable cause of an effect or event, rely instead
on finding a key difference. Why might it be important
to determine cause? If you believe that one event (a
cause) is somehow related to another event (an effect),
you may want to either reproduce that relation, which
would again cause the effect, or in some cases prevent
the relation form recurring, thereby preventing the
effect.
For example, every time you study hard for a test,
you get a good grade. If you want to keep getting good
grades, you want to know if there is a link between
studying hard and getting good grades. When you can
determine cause and effect, you can repeat the effect.
In this case, that means figuring out that the studying
really does result in good grades. To continue to get
good grades, therefore, you need to continue to study
hard for your tests.
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