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Wednesday, October 19, 2011

To Cut Down a Tree With a Herring, Part 2

You thought I’d forgotten, but no such luck, dear reader.  We’re back with day two of A Leisurely Glance at Logic.  I’ll paraphrase from the website of the writing center at UNC to preface: when making an argument, you need premises that are true, that actually support your conclusion, that are adequate in their totality to support the argument, and that are specific.

Fallacies are the places where your premises or their connection to your main argument fall apart.

Here are two of the most common:

  1. The conclusion drawn from inadequate personal experience.  Like, "Most reputable medical journals and studies have ruled out a link between MMR vaccines and Autism, but my friend's kid showed symptoms after getting a shot, so there MUST be a connection."  Whether or not there is a connection is not the point; carefully designed studies use large samplings and control groups and try to rule out other variables, so you need a lot more evidence than your friend’s gut.  This is a hasty generalization from a small sample, but it’s also a post hoc fallacy, or assuming causation because something happens after something else.

  1. A cruddy syllogism.  A syllogism is the kind of proof where you take one big [true] statement, and then one smaller one, and from them draw a concluding statement.  Like:  All vegetables are food. Corn is a vegetable.  So...Corn is a food.  A cruddy syllogism is one where a false statement mucks up the flow, and renders the conclusion invalid.  Like: All Italians are criminals.  The Wife of Leisure is Italian.  The Wife of Leisure is a criminal.  Now, I may be a criminal, but you wouldn't know it by this logic, because you can hardly prove that all of us Wops are truly living lives of crime.  Also, I’m only half Wop.  There are lots of other ways you can screw up your syllogistic argument, but this is one of the most common, and after all, this is a leisurely approach to logic.
That’s enough for today but for a disclaimer.  I actually love a good generalization.  They are useful and the less sensitive among us recognize that they are often rooted in truth (which is why my thoroughly patriotic Syrian-American friend is not offended when he is often singled out at airports for a pat down.)  But if you know that your conclusion rests on a loose generalization, just put it out there.  “I know not all Italians are criminals, but I still wonder about my neighbor who calls himself Giuseppe the Boot…”  This way you’re covered.

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