Another Example
EXAMPLE 2a
Green says:
Most economists are not very good writers.
Maynard is an economist.
Therefore, Maynard probably is not a very good writer.
Even if we accept the first two statements, we could reject the third, if we had reasons to believe that Maynard is an exception to the general rule. The argument is defeasible, which means that while (on the one hand) it is somewhat persuasive as a general matter, nevertheless (on the other hand) it is fallible. We can conceive of a counterargument that could undercut it. Here is an example of an undercutting counterargument:
EXAMPLE 2b
Brown says:
That's not true. Maynard is an exception.
I have read his poetry, and it is extremely fine.
Here Brown argues from personal experience, and the argument undercuts the presumption that Maynard is a poor writer. Now, an undercutting argument does not automatically win. As a rule, an undercutting argument will also be a defeasible argument, which means that it can in turn be undercut. In this case, Brown's argument is fairly weak, since it relies strongly on Brown's personal judgment of the quality of Maynard's poetry; another person, who had also read Maynard's poetry, might undercut Brown's response by offering a contrary opinion. But if Green has not read it, this response would not be available to Green, and Green is at the disadvantage. Let us see another way this dialog might play out:
EXAMPLE 2c
Gold says:
I have read it, too, and I disagree. Maynard's verse has no meter or rhyme -- it's quite bad.
Brown says:
Well, that's your opinion. But as a Professor of Literature, with many publications in verse criticism, I can tell you that meter and rhyme are not all there is to poetry. I believe most recognized critics of modern verse would agree with me in pronouncing Maynard's work good.
In example 2c, Gold undercuts Brown's position with, essentially, a "my opinion is as good as your opinion" claim, and Brown attempts in turn to undercut that claim by appealing to her own expert knowledge and a claimed consensus (on standards for judging poetry) in a community of experts. This sort of reason may be very powerful in some contexts (for example, a court of law) and less persuasive in others (for example, in a discussion of laboratory science, where replication of experiments is an important criterion). Whether it will be persuasive in this case depends on how reliable we regard experts in this field as being and whether we believe the claim that Brown's judgment reflects a consensus of experts.
