Let’s turn to a few examples of vague and ambiguous terms. For variety, let’s look at the word ‘bald’ as it occurs in the following (slightly silly) context.
1. [bald]: My friend, Andrew, has a receding hairline. He has not lost all of his hair, but he has lost quite a bit of it. If Andrew found himself in a room with Tom Cruise, who has a full head of hair, the sentence “Andrew is bald.” would appear true, but if he found himself in a room with John Malkovich, who is completely bald, it would appear false. Why is the same sentence true in the first case, but false in the second?
[Activity] Come up with an answer for the question above. Then, with a partner, discuss your respective answers. Try to come up with a few more examples of scenarios where the same sentence containing a vague term comes out true in one case and false in another. What do these examples have in common?
2. This cold is killing me!
Suppose a speaker who has a terrible cold expresses the above sentence in a place with below freezing temperatures. As before, without some further explanation, the meaning of this sentence is not completely clear; in other words, if we were friends with the speaker who expresses this sentence to us, we could reasonably ask if they mean that their illness is killing them or the outside temperature is killing them.
[Activity]: If the same sentence in Example 2. is expressed by a speaker with a terrible cold in a very warm place in the summer, is the word ‘cold’ still ambiguous?
Sometimes, syllogisms are unsound because of vague or ambiguous terms. This can happen even if the syllogism is valid and its premises are true. Consider the following argument:
Premise 1 (P1): All famous actors are stars.
Premise 2 (P2): All stars are celestial bodies.
Conclusion (C): All famous actors are celestial bodies.
[Activity]: Before we look at the explanation for why this argument is actually unsound, try to figure it out for yourself. What’s going on with the term ‘star’? [Hint: think of ambiguity as we discussed it in this lesson].
This argument uses two different meanings of the word ‘star’: one in each premise. This is an instance of ambiguity. The term ‘star’ is ambiguous because it is used to refer to different categories in the world during the same syllogism.
[Activity]: Review: Is the argument above valid? Is it sound? Discuss with a partner!