3 4 6C H A P T E R 1 7 ■ R e f u t a t i o nthat it would be good if nobody else shot their children by mistake. So far, so
good. Notice, however, that this latest argument, (1**)–(3**), does not have
the same form as the original argument, (1)–(3), because (2**) and (3**) are
about what is good and what ought to be law, whereas (2) and (3) are about
what is bad and what ought not to be law. (3) includes a negation that is
missing in (3**).
The next question is whether this disanalogy is important. If not, the latest
bumper sticker still might refute the original one. The NRA, however, might
argue that this difference is important. The fact that a law has bad effects
overall does show that the law should not be passed, whereas the fact that
a law would have good effects overall is not enough to show that the law
should be passed, since the law still might violate individual rights that can-
not be overridden by good effects on others. This claim is controversial, but,
if it can be defended, then this parallel argument, (1**)–(3**), fails to show
that the original argument, (1)–(3), is invalid. More generally, then, a refuta-
tion by parallel reasoning works only if the two arguments really do have
relevantly similar structures—that is, only if one argument really is just like
the other in relevant respects.
In sum, the method of refutation by parallel reasoning can be used to
show that an argument is invalid by presenting another argument with es-
sentially the same form in which the inference takes us from obvious truths
to an obvious falsehood. In response to such an attack, a defender of the
original argument has three main options. The defender might- deny that the conclusion of the parallel argument is false,
- deny that the premises of the parallel argument are true, or
- deny that the supposedly parallel argument really has essentially the
same form as the original argument.
If any of these responses is justified, then the attempt to refute the original
argument by parallel reasoning fails.
This procedure is admittedly imprecise. There will sometimes be dis-
putes about whether the premises of the parallel argument really are true,
or clearly true, and whether the conclusion of the parallel argument really is
false, or clearly false. Moreover, we have given no general explanation of the
notion that two arguments have the same basic form. Some forms of argument
were discussed in previous chapters, but they are only part of the story. We
have not discussed and cannot discuss all possible forms of argument. Yet it
remains a fact that people can often see that two arguments have the same
essential form and, through seeing this, decide that an argument presented
to them is invalid. This ability is the basis of sound logical judgment. It is
also the basis of wit. It is at best mildly funny to say that if God had wanted
us to fly, He would have given us wings. You have to be fairly clever to reply
at once, “If God had wanted us to stay on the ground, He would have given
us roots.”
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