Читать книгу The Philosopher's Toolkit - Julian Baggini, Julian Baggini - Страница 19

For most of us, the idea of a ‘conclusion’ is as straightforward as a philosophical concept gets. A conclusion is just that with which an argument concludes, the product and result of an inference or a chain of inferences, that which the reasoning claims to justify and support. What about ‘premises’, though? Premises are defined in relation to the conclusion. They are, of course, what do the justifying. There is, however, a distinctive and a bit less obvious property that all premises and conclusions must possess.

In order for a sentence to serve either as a premise or as a conclusion, it must exhibit this essential property: it must make a claim that is either true or false. A sentence that does that is in logical terms called a statement or proposition.

Sentences do many things in our languages, and not all of them possess that property and thence not all of them are statements. Sentences that issue commands, for example (‘Forward march, soldier!’), or ask questions (‘Is this the road to Edinburgh?’), or register exclamations (‘Wow!’), are neither true nor false. Hence, it’s not possible for sentences of those kinds to serve as premises or as conclusions.

This much is pretty easy, but things can get sticky in a number of ways. One of the most vexing issues concerning arguments is the problem of implicit claims. That is, in many arguments, key premises or even the conclusion remain unstated, implied or masked inside other sentences. Take, for example, the following argument: ‘Socrates is a man, so Socrates is mortal.’ What’s left implicit is the claim that ‘all men are mortal’. Arguments with unstated premises like this are often called enthymemes or enthymemetic.

It’s also the case that sometimes arguments nest inside one another so that in the course of advancing one, main conclusion several ancillary conclusions are proven along the way. Untangling arguments nested in others can get complicated, especially as those nests can pile on top of one another and interconnect. It often takes a patient, analytical mind to sort it all out (just the sort of mind you’ll encounter among philosophers).

In working out precisely what the premises are in a given argument, then, ask yourself first what the principal claim is that the argument is trying to demonstrate. Then ask yourself what other claims the argument relies upon (implicitly or explicitly) in order to advance that demonstration. Sometimes certain words and phrases will explicitly indicate premises and conclusions. Phrases like ‘therefore’, ‘in conclusion’, ‘it follows that’, ‘we must conclude that’, and ‘from this we can see that’ often indicate conclusions. (‘The DNA, the fingerprints, and the eyewitness accounts all point to Smithers. It follows that she must be the killer.’) Words like ‘because’ and ‘since’, and phrases like ‘for this reason’ and ‘on the basis of this’, on the other hand, often indicate premises. (For example, ‘Since the DNA, the fingerprints, and the eyewitness accounts all implicate Smithers, she must be the killer.’)

Premises of an argument, then, compose the set of claims from which the conclusion is drawn. In other sections, the question of precisely how we can justify the move from premises to conclusion will be addressed in more in more detail (see 1.4 and 4.7). But before we get that far, we must first ask, ‘What justifies a reasoner in entering a premise in the first place?’