Let’s get tough! Analyzing those arguments

12 Aug

Let’s imagine you’ve heard an argument that just doesn’t sound right,

but you can’t put your finger on the reason.  The major and minor premise are even

true statements!  So what could be wrong?

Formal Logic rules to the rescue!  Applying a few simple tests to an argument can help you determine if it is indeed ‘valid’, that is in the correct form.  (remember that formal logic doesn’t deal with the truth of propositions, but the structure of an argument)

Today we’re going to look at the first 2 of 7 rules that are easy to use in analyzing the structure of an argument.

Rule # 1 – Three and only 3 terms

       Some boys are strong

       My brother is a baseball player

       Therefore, my brother is strong

Let’s count the terms.  Remember that a term is the number of words necessary to describe a concept. Terms must contain at least one word and can have several (mint chocolate chip ice cream is one term containing 5 words).   

When we identify and label terms, we start at the bottom of the syllogism and label the terms in the conclusion

Our conclusion above is:     Tf, my brother (minor term) is strong (major term)

Next, we label the same terms elsewhere in the syllogism.  The unlabeled term will then be the middle term

As we look for that middle term, we see our problem, which term do we label as the middle term?  We have two remaining terms and they are different!

      Some boys ( ? term)  are strong (major term)

      My brother (minor term) is a baseball player ( ? term)

      Tf, my brother (minor term) is strong (major term)

You can see our problem: we have 2 terms, both different (boys, baseball player) so we don’t know WHICH one will be the middle term (the 3rd official term after we have identified the minor and major terms).

So we can say with assurance, this syllogism is NOT valid because it has 4 terms.


Rule # 2 – the middle term must not be in the conclusion

Again, we start to label ‘bottom up’. (this takes a while to become automatic for we are conditioned to start at the top and label down )

      Some baseball players are strong

      My brother is strong

      Tf, my brother is strong and a baseball player

We barely get started  labeling the conclusion and we see that we have a problem.  Not only are there 3 terms in that one proposition (brother, strong, baseball player), but we have a term, ‘strong’, that shows up 3 times.  That is the tip-off that our middle term strong’ is in the conclusion.  The entire syllogism is convoluted.  So we shout out: “INVALID!!”

Next time, when we look at Rules 3 & 4, we will measure how far an attribute or term extends.  We will be asking questions like,

  • Are we talking about the category or set of ALL baseball players?
  • Are we talking about the category or set of ALL that which is strong?

If we say ‘yes’, then we say that a term is ‘distributed’ – that the quality in question applies to ALL, or that we are addressing ALL the members of a set.

In the meantime, watch your words and how others use words.  We must strive to be precise with our language if we intend to communicate clearly and with as few words as possible.

Excessive and unclear verbiage is wearying!  

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