Arguments and Validity
The notion of an argument is used in such a variety of contexts that it cannot by itself provide a suitable basis for an abstraction to a logical test of cogency. People are sometimes said to be having an argument when they are simply shouting at one another. Again, a certain kind of movie may be said to be an argument against war. In order to have a firm basis for abstracting logical problems, logicians have found through experience that it is helpful to define an argument as a certain kind of sequence of sentences. The sentences of an argument must all be such that if certain facts obtain, they are true, and if these facts do not obtain, they are false. Since the relevant facts may not be known when an argument is advanced, it may not be known whether or not the sentences in an argument are true or false. Nevertheless, each sentence in an argument must be of the kind which would be true or false if we came to know certain related facts. A particular sentence used on some occasion to make a claim that would be true or false if certain facts were known will, for the time being, be called an assertion. An assertion is not just a sentence, but a sentence used in some context to make a factual claim. For ex?ample, if you find a sentence written on a piece of paper left lying around by someone, that sentence is just a sequence of English words (let us say) until it is discovered what the author was doing when he wrote the sentence down. An actual argument will clearly be a sequence of assertions, but we let the sentences used to make these assertions constitute the basis for abstraction to a logical form. In doing this, we will switch back and forth between talk about sentences and talk about the assertions which they would be used to make in some context.
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