How to Win Every Argument: The Use and Abuse of Logic (2006)

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Division 53

Spinach is good for growing children. Eat it up.
(But beware of the construction which says that 'all good children do
such and such'. Your progeny might slip out of the group in question
by recognizing themselves as bad.)

Division

The doppelgànger of the fallacy of composition is that of division.
When we attribute to the individuals in a group something which
is only true of the group as a unit, we fall into the fallacy of division:


Welsh-speakers are disappearing. Dafydd Williams is a Welsh-speaker,
therefore Dafydd Williams is disappearing.
(No such luck. Only the class of Welsh-speakers is disappearing, not
the individuals who make it up.)

We commit the fallacy by sliding our adjectives to describe the
whole over onto the individuals who comprise it:


The Icelanders are the oldest nation on earth. This means that Bjork
must be older than other pop stars.
(And before you go to her house, remember that the Icelandic people
live surrounded by hot mud and active volcanoes.)

As with composition, the source of the error in the fallacy of
division lies in the ambiguity of collective nouns. Both of these
are a form of the fallacy of equivocation, in that it is the different
meanings of the noun which upset the validity of the argument.
It would only be valid if the same meaning were retained
throughout. (The gospels are four in number. St Mark's is a
gospel, so St Mark's is four in number.)
Division is often used fallaciously to confer upon an individual
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