1 8 0C H A P T E R 8 ■ A r g u m e n t s T o a n d F r o m G e n e r a l i z a t i o n sHere we have drawn an inductive inference from the characteristics of
observed ravens to the characteristics of all ravens, most of which we have
not observed. Of course, the premise of this argument could be true, yet the
conclusion turn out to be false. A raven that has not yet been observed might
be albino. The obviousness of this possibility suggests that someone who
gives this argument does not put it forth as valid, so it is not a deductive
argument. Instead, the premise is put forth as a reason or support for the con-
clusion. When an argument is not claimed to be valid but is intended only to
provide a reason for the conclusion, the argument is inductive.
Because inductive arguments are supposed to provide reasons, and reasons
vary in strength, inductive arguments can be evaluated as strong or weak, de-
pending on the strength of the reasons that they provide for their conclusions.
If we have seen only ten ravens, and all of them were in our backyard, then the
above argument gives at most a very weak reason to believe that all ravens are
black. But, if we have traveled around the world and seen over half the ravens
that exist, then the above argument gives a strong reason to believe that all
ravens are black. Inductive arguments are usually intended to provide strong
support for their conclusions, in which case they can be criticized if the support
they provide is not strong enough for the purposes at hand.
The most basic distinction, then, is not between two kinds of argument
but is instead between two standards for evaluating arguments. The de-
ductive standard is validity. The inductive standard is strength. Arguments
themselves are classified as either deductive or inductive in accordance with
the standard that they are intended or claimed to meet.
There are several important differences between deductive and inductive
standards. One fundamental feature of the deductive standard of validity is that
adding premises to a valid argument cannot make it invalid. The definition of
validity guarantees this: In a valid argument, it is not possible for the premises to
be true without the conclusion being true as well. If any further premises could
change this, then it would be possible for this relationship not to hold, so the
argument would not be valid after all. Additional information might, of course,
lead us to question the truth of one of the premises, but that is another matter.
The situation is strikingly different when we deal with inductive argu-
ments. To cite a famous example, before the time of Captain Cook’s voyage
to Australia, Europeans had observed a great many swans, and every one of
them was white. Thus, up to that time Europeans had very strong inductive
evidence to support the claim that all swans are white. Then Captain Cook
discovered black swans in Australia. What happens if we add this new piece
of information to the premises of the original inductive argument? Provided
that we accept Cook’s report, we now produce a sound deductive argument
in behalf of the opposite claim that not all swans are white; for, if some swans
are black, then not all of them are white. This, then, is a feature of the induc-
tive standard of strength: No matter how strong an inductive argument is,
the possibility remains open that further information can undercut, perhaps
completely, the strength of the argument and the support that the premises97364_ch08_ptg01_177-194.indd 180 15/11/13 10:44 AM
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