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II

H o w t o E v a l u a t e

A r g u m e n t s : D e d u c t i v e

S t a n d a r d s

After isolating, laying out, and filling in an argument, the next step is to determine

whether that uncovered argument is any good. This assessment, like other evaluations,

requires standards. There are two main standards for evaluating arguments: the

deductive standard of validity and the inductive standard of strength. Part II (which

includes Chapters 6 and 7) will investigate the deductive standard of validity. Part III

(which includes Chapters 8–12) will then explore the inductive standard of strength.

We already saw in Chapter 5 that an argument is valid in our technical sense if

and only if it is not possible that its premises are true and its conclusion false. That

standard sounds simple, but it is not so easy to say how to determine whether this

combination of truth values is or is not possible in a particular case. Sometimes the

validity of an argument can be seen simply by looking at the premises and conclu-

sion viewed as whole propositions. That is the approach of propositional (or senten-

tial) logic, which is the topic of Chapter 6. Another possibility is that the validity of

an argument can be seen only by looking inside premises and conclusions to their

parts, including their subjects and predicates. That is the approach of categorical (or

syllogistic) logic, which is the topic of Chapter 7.

These relatively simple examples of formal logic do not, of course, exhaust the

possibilities. There are many more kinds of formal logic. Many arguments remain

valid, even though their validity is not captured by either propositional or categori-

cal logic. That creates problems that we will face throughout Chapters 6 and 7. Still,

by exploring some simple ways in which arguments can be valid by virtue of their

form alone, we can gain greater insight into the nature of validity and, thereby, into

the standards for assessing arguments.

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