How to Think #2: BARBARA, Cont.

Let's cover a couple more points about syllogisms using Barbara before we move on to the next one.

First, here is another example of Barbara:

1. All politicians tell lies
2. All presidential candidates are politicians
3. Therefore, all presidential candidates tell lies.

Now look at this one:

1. All college professors are intelligent
2. Doctor Smith is a college professor
3. Therefore, Doctor Smith is intelligent.

This second example looks different from the first because the second line is about one person rather than "all" the members of a group. But that's OK. Whether the second line is about a group or an individual, the syllogism is still Barbara and still valid.

As we have already stressed, if the premises of a valid syllogism are true, then the conclusion MUST be true. But if the premises are false that does not prove the conclusion is false. It just means we don't know.

One more thing to watch out for. Sometimes people get confused when a conclusion is true and assume that the syllogism must prove the conclusion.

But consider this:

1. Everything Joe owns is a car
2. A Toyota Camry is one of the things Joe owns.
3. Therefore a Toyota Camry is a car.

Now we may believe that it is true that a Toyota Camry is a car but this syllogism does not prove it. The syllogism is an example of Barbara so we know it is valid. But the first premise is not true so the syllogism is not sound and does not prove its conclusion. We may know through some other means that a Toyota Camry is a car but this particular argument is a failure.

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Copyright © 2016 by Joseph Wayne Gadway