The Language of Argument

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I n d u c t i o n v e r s u s D e d u c t i o n

give to the conclusion. Because inductive strength and inductive arguments

can always be defeated in this way, they are described as defeasible. Valid

deductive arguments do not face a similar peril, so they are called indefeasible.

A second important difference between inductive and deductive stand-

ards is that inductive strength comes in degrees, but deductive validity does

not. An argument is either valid or invalid. There is no question of how much

validity an argument has. In contrast, inductive arguments can be more or

less strong. The more varied ravens or swans we observe, the stronger the

inductive arguments above. Some inductive arguments are extremely strong

and put their conclusions beyond any reasonable doubt. Other inductive ar-

guments are much weaker, even though they still have some force.

Because of the necessary relationship between the premises and the conclu-

sion of a valid deductive argument, it is often said that the premises of valid

deductive arguments (if true) provide conclusive support for their conclusions,

whereas true premises of strong inductive arguments provide only partial

support for their conclusions. There is something to this. Because the premises

of a valid deductive argument necessitate the truth of the conclusion, if those

premises are definitely known to be true, then they do supply conclusive rea-

sons for the conclusion. The same cannot be said for inductive arguments.

It would be altogether misleading, however, to conclude from this that in-

ductive arguments are inherently inferior to deductive arguments in supplying

a justification or ground for a conclusion. In the first place, inductive arguments

often place matters beyond any reasonable doubt. It is possible that the next pot

of water will not boil at any temperature, however high, but this is not some-

thing we worry about. We do not take precautions against it, and we shouldn’t.

More important, deductive arguments normally enjoy no advantages

over their inductive counterparts. We can see this by comparing the two fol-

lowing arguments:

Deductive Inductive

All ravens are black. All observed ravens are black.

[ If there is a raven on top

of Pikes Peak, it is black.

[ If there is a raven on top of

Pikes Peak, it is black.

Of course, it is true for the deductive argument (and not true for the induc-

tive argument) that if the premise is true, then the conclusion must be true.

This may seem to give an advantage to the deductive argument over the in-

ductive argument. But before we can decide how much support a deductive

argument gives its conclusion, we must ask whether its premises are, after all,

true. That is not something we can just take for granted. If we examine the

premises of these two arguments, we see that it is easier to establish the truth

of the premise of the inductive argument than it is to establish the truth of the

premise of the deductive argument. If we have observed carefully and kept

good records, then we might be fully confident that all observed ravens have

been black. On the other hand, how can we show that all ravens (observed

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