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We've all probably made easily avoidable errors of logic. Therefore,
everyone will want to read an article like this in order to avoid
doing so in the future.
There are, of course, several logical problems with the preceding
two sentences (we're so predictable), but we'll only mention one:
the concluding (second) sentence assumes a premise which probably
isn't true, specifically, that we all care about not making logical
errors. If you don't care about such things, you are an execrable
cretin and may run along and read about homebrewing
or tattoos. If, however, you
do care, please read on and learn how to be more logical.
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When
we talk about logic in this article, we aren't talking about
symbolic or formal logic. We're talking about the logical rules
that govern the making and evaluation of arguments. When we talk
about arguments, we mean a premise or series of premises that is
or are intended to lead to a conclusion. A "non sequitur"
is when such good intentions fail.
"Non
sequitur" is Latin for "it does not follow." To
say that an argument is a non sequitur is simply to say that the
conclusion does not follow from the premises. This term would
apply to any argument that has a conclusion that doesn't
follow from its premises. It is often used, however, to refer
to particular types of arguments that clearly do not follow from
their premises and never could.
For
example, any argument that takes the following form is a non sequitur:
Step
1: If A then B |
If
I am a goat, I am a hoofed creature. |
Step
2: B |
I
am a hoofed creature. |
Step
3: Therefore, A |
Therefore,
I am a goat. |
It is clear that this argument does not follow. Even if the premises
and conclusion were all true, the conclusion is not a necessary
consequence of the premises. This sort of non sequitur is also
called "affirming the consequent."
Another
common non sequitur is this:
Step
1: If A then B |
If
I am in Rome, I am in Italy. |
Step
2: Not A |
I
am not in Rome. |
Step
3: Therefore, not B |
Therefore,
I am not in Italy. |
The speaker could be in all kinds of other places in Italy, worrying
way less about pickpockets and having a great time. This sort
of non sequitur is called "denying the antecedent."
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Go
on to Step 2: DO
NOT BEG THE QUESTION --> |
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