writing to convince
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CRITICAL THINKING & WRITING
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WHAT IS AN ARGUMENT?
An argument (a piece of reasoning) is a set of
statements, one of which (the conclusion) is
maintained to be true on the strength of the
others (the premises).
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WHAT IS AN ARGUMENT?
Argument = premises + conclusion
Every argument has exactly one conclusion and
at least one premise
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RECOGNIZING PARTS OF
ARGUMENTS
Phrases that indicate a conclusion
Therefore
So
Thus
it follows that
as such
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RECOGNIZING PARTS OF AN
ARGUMENT
Phrases that indicate a premise
Since
Because
As
For
due to the fact that
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ENTHYMEMES
An enthymeme is an argument, one of whose
premises (or perhaps even the conclusion) is
implicitly suppressed, though intended as
present
Example:
John will die one day, because he is a man.
Whats the missing premise?
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DEDUCTION VS. INDUCTION
An argument is said to be deductive in the casethat the conclusion is meant (by the arguer) tobe guaranteed by the premises (whether the
premises are true or not is a different matter). An argument is said to be inductive in the case
that the conclusion is meant (by the arguer) tobe made probable by the premises (whetherthe premises are true or not is a differentmatter).
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EXAMPLES OF DEDUCTIVE
ARGUMENTS
Either John or Peter broke the glass. John did
not do it. So Peter did it.
John is taller thanP
eter.P
eter is taller than hisfather. So John is taller than Peters father.
Either John ofPeter is the King of Singapore.
John is not. So Peter must be the King of
Singapore.
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EXAMPLES OF INDUCTIVE
ARGUMENTS
It has been raining for five days in a row. There
are dark clouds now. I conclude that it will rain
again today.
There are one million tickets in the lottery.
There is only one prize. I only have one ticket. I
conclude that I wont win the prize.
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VALIDITY AND STRENGTH
If the conclusion of a deductive argument isindeed guaranteed by the premises, then theargument is said to be deductively valid.
Otherwise, it is deductively invalid.
If the conclusion of an inductive argument is
indeed made probable by the premises, thenthe argument is said to be inductively strong.Otherwise, it is inductively weak.
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ARE THESE DEDUCTIVE ARGUMENTS VALID OR
INVALID?
If it rains, itll flood. If it floods, well drown. So ifrains, well drown.
You wont win unless you try. You wont try unless
you dream. So you wont win unless you dream. Either John or Peter will be here. Either Peter or
Mary will be here. So either John or Peter will behere.
No horses are found in Country A. Country A is
found to the north of Country B. So no horses arefound in the north of Country B.
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ARE THESE INDUCTIVE ARGUMENTS STRONG OR
WEAK?
Every century in the past century has been
witness to at least one major war. So at least
one major war will be fought this century.
Youre wearing a red shirt today. So youll be
attacked by a bull.
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