The "No True Scotsman" Fallacy

For Kathleen's edification, here are two of the explanations one finds by doing
a web search on "No True Scotsman."  There are hundreds, and they all say the
same things -- although the examples may differ.

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"No True Scotsman" is two logical errors at the same time: post hoc and begging
the question.

The error is named after a specific example. There is a story where a Scotsman
reads a newspaper story about a horrible murder in London, and proudly states
that this sort of thing can only happen in England because no Scotsman would
ever be so deranged. Later, the news reports that the murderer was just off the
train from Glasgow, and lived in Scotland all his life. The Scotsman reading
the article revises his statement, saying that no *true* Scotsman would do such
a thing. 

The two problems with this argument are 1) the definition of a Scotsman is now
totally redefined, after the first assertion was proven so obviously false,
without good reason, and 2) the definition of a Scotsman will always now
exclude murderers from Scotland. Henceforth, it will always be true that
Scotland produces no murderers, if murderers are no longer Scotsmen.
Technically, if the whole country went berserk and killed each other, the one
guy left standing would represent true Scots. 

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Fallacy Name:
No True Scotsman Fallacy 

Category:
Fallacy of Ambiguity, Fallacy of Presumption 

Explanation:
This is actually a combination of several fallacies, but since it rests
ultimately on shifting the meaning of terms -- a form of equivocation -- and
begging the question, it receives special attention. 

The name "No True Scotsman" comes from an odd example involving Scotsmen: 

1. Suppose I assert that no Scotsman puts sugar on his porridge. You counter
this by pointing out that your friend Angus likes sugar with his porridge. I
then say "Ah, yes, but no *true* Scotsman puts sugar on his porridge." 

Obviously the original assertion about Scotsmen has been challenged quite well,
but in attempting to shore it up the speaker uses an ad hoc change combined
with a shifted meaning of the words from the original. 

Examples and Discussion:
How this fallacy can be used is perhaps easier to see in this example from
Anthony Flew's book Thinking about Thinking - or do I sincerely want to be
right?: 

2. Imagine Hamish McDonald, a Scotsman, sitting down with his Press and Journal
and seeing an article about how the 'Brighton Sex Maniac Strikes Again'. Hamish
is shocked and declares that "No Scotsman would do such a thing". The next day
he sits down to read his Press and Journal again and this time finds an article
about an Aberdeen man whose brutal actions make the Brighton sex maniac seem
almost gentlemanly. This fact shows that Hamish was wrong in his opinion but is
he going to admit this? Not likely. This time he says, "No true Scotsman would
do such a thing." 

You can change this to any other bad act and any group you like to get a
similar argument. A common one which is often heard when a religion or
religious group is criticized is: 

3. Our religion teaches people to be kind and peaceful and loving. Anyone who
does evil acts certainly isn't acting in a loving manner, therefore they can't
really be a true member of our religion, no matter what they say. 

But of course, the exact same argument can be made for any group -- a political
party, a philosophical position, etc. Here is a real life example of how this
fallacy can be used: 

4. Another good example is abortion, our government has such a small Christian
influence that the courts have ruled it's OK to kill babies now. The people who
support legalized abortion but claim to be Christians don't really follow Jesus
-- they have lost their way. 

In an effort to argue that abortion is wrong, it is assumed that Christianity
is inherently and automatically opposed to abortion (begging the question). In
order to do this, it is further argued that no one who supports legalized
abortion -- for any reason -- can really be a Christian (equivocation through
an ad hoc redefinition of the term "Christian"). 

Similar arguments are made regarding a host of controversial political, social
and economic questions: real Christians can't be for (or against) capital
punishment, real Christians can't be for (or against) socialism, real
Christians can't be for (or against) drug legalization, etc. We even see it
with atheists: real atheists can't have irrational beliefs, real atheists
cannot believe in anything supernatural, etc.

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I hope this helps.

:-)

Jenny

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