Minds and Computers : An Introduction to the Philosophy of Artificial Intelligence
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patterns from environmental stimulus and recognising when these
patterns obtain again, even when they only partially obtain, or when there is some variation in the pattern. This is an important insight and one which we will return to discuss at great length in Chapter 19. For the moment, note that this is not ipso facto an argument against computationalism, but it does place an explanatory burden on the computationalist – the burden being to give a computational account of this cognitive capacity. Now that we have compared, at least in rudimentary fashion, the way humans play complex games with the way computers can be pro- grammed to play these games, it is time to turn our attention to the human rational and linguistic capacities. 131 C H A P T E R 1 3 MACHINE REASONING In this chapter we are going to begin to investigate the rational cap- acity – the ability to reason. A thorough survey of automated rea- soning methods would require dedicated volumes. We’re going to concentrate on one kind of automated reasoning project which suits our purposes well – the design of expert systems. We’re going to see how we might recreate, with the use of formal systems, the reasoning processes of a human expert in a particular domain. Before we do so, we will first need to make clear some concepts and terminology involved in the study of logic. 13.1 LOGIC AND DEDUCTION The first thing to appreciate is that there is a distinction between logic and logics. Logic is a research tradition whose objects of investigation are logics. These logics are formal systems and there are very many of them. The aim of logics is to formally encode relations of entailment or logical consequence. In other words, logics are formal systems which provide methods for determining what follows from what as a matter of logical form. Another important point is that, like all formal systems, logics are concerned only with formal properties. While it is the case that elem- ents of logics are interpretable as meaning something, issues of meaning never have any bearing on determinations of logical conse- quences. In other words, whether or not something follows logically from some other things is entirely a question of their respective logical forms. The relevance of this will become apparent in exercises later in this chapter. I don’t expect you to yet have an understanding of precisely what logical form is or how to discern logical forms. I don’t intend this to 132 be a fully fledged introduction to logic so I’ll reserve further discus- sion concerning this for the next section where we’ll see some simple examples. Given that logics are formal systems, you should be wondering what the states are and what the rules are. For our purposes, states can be thought of as sets of statements. Rules of logics are such that given an input state containing some statements of a certain form, we can derive new statements of a certain form to add to the output state. This process of applying logical rules to sets of statements to gen- erate novel statements is the process of deduction. While we will be concentrating on deduction in this chapter, it is important to realise that there are other distinct kinds of reasoning. We’ll revisit this issue at length in Chapter 15 and again in Chapter 19 but for the moment let’s just briefly consider the distinction between deduction and induction. Induction is the form of reasoning employed by empirical science. Inductive proof is rather a di fferent thing from deductive proof. A deductive proof is a demonstration – of the kind we will see in the fol- lowing section – that certain statement forms can be derived from other statement forms according to certain logical rules. A typical Download 1.05 Mb. Do'stlaringiz bilan baham: |
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