Logical Gal spots 2 fallacies in one syllogism

4 Oct

The other day I was listening to a radio program recounting a debate that had taken place in Australia.

One of the two debaters apparently resorted to name-calling and sought to be clever by doing so within a verbal syllogism.

And in the ensuing radio discussion about the quality of the debate, a listener pointed out there was a logic error within the syllogism.

Here is the syllogism (unfortunately it was intended to demean)

All mammals exhibit homosexual behavior

Joe is a mammal

Tf, Joe exhibits homosexual behavior

Can you identify the error?  You don’ t have to know anything about Joe’s sexual preferences to notice the problem.

Remember that a syllogism is limited in form by the requirement to have exactly 3 terms.  What are the terms in this one?

  1. mammals
  2. (that which)  exhibits homosexual behavior
  3. Joe

“ So…….??”  you say.

Here’s the problem: the term ‘mammals’  is actually used equivocally to mean two different concepts.

In premise 1, the term mammals really means species of mammals

So then in premise 2, mammals is used as a particular MEMBER of a species of mammals.

If we were to accurately state the premises and conclusion of the one advancing the argument, we would quickly see that he has used clever wording to cover up his Fallacy of Equivocation.  To reach his conclusion, he has to employ more than the 3 terms. (I’ve colored each term – only ‘ Joe’  is used twice.  We actually have 5 terms in this syllogism.

P1 – All species of mammals are species that have members that exhibit homosexual behavior

P2 – Joe is a member of a species of mammals that exhibits homosexual behavior

Tf – Joe is a mammal that exhibits homosexual behavior

And if that weren’t enough, he also commits the Fallacy of Division.  This happens when we assume that a quality of the group applies equally to every member of a group.

If we say “ Texas A&M sure is a passing team” in the sense that they pass the ball  a lot, it does not follow that every member of that team is a higher-than-average passer!

It may be that the Jones family is very artistic.   But Billy Jones is not necessarily artistic himself.  He might take after his great-great grandfather who played for Texas A& M!

A cake may be tasty, but each ingredient is not.  Have you ever snacked on butter? Do you see the fault in the reasoning?

Back to Joe and the name-calling debater.  Not only did his accuser have to cobble together multiple terms and then hide them, he also committed the Fallacy of Division and presumed to announce something about Joe that stretched beyond the known facts.

Remember, whoever makes the claim has to be able to defend his thinking!

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