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The philosophy of science can usefully be divided into two broad areas. On the one hand is the epistemology of science, which deals with issues relating to the justification of claims to scientific knowledge. Philosophers working in this area investigate such questions as whether science ever uncovers permanent truths, whether objective decisions between competing theories are possible and whether the results of experiment are clouded by prior theoretical expectations. On the other hand are topics in the metaphysics of science,topics relating to philosophically puzzling features of the natural world described by science. Here philosophers ask such questions as whether all events are determined by prior causes, whether everything can be reduced to physics and whether there are purposes in nature. You can think of the difference between the epistemologists and the metaphysicians of science in this way. The epistemologists wonder whether we should believe what the scientists tell us. The metaphysicians worry about what the world is like, if the scientists are right.
Much recent work in the epistemology of science is a response to the problem ofinduction. Induction is the process whereby scientists decide, on the basis of various observations or experiments, that some theory is true. At its simplest, chemists may note,say, that on a number of occasions samples of sodium heated on a Bunsen burner have glowed bright orange, and on this basis conclude that in general all heated sodium will glow bright orange. In more complicated cases, scientists may move from the results of a series of complex experiments to the conclusion that some fundamental physical principle is true. What all such inductive inferences have in common, however, is that they startwith particular premises about a finite number of past observations, yet end up with a general conclusion about how nature will always behave. And this is where the problem lies. For it is unclear how any finite amount of information about what has happened in the past can guarantee that a natural pattern will continue for all time.
After all, what rules out the possibility that the course of nature may change,and that the patterns we have observed so far turn out to be a poor guide to thefuture? Even if all heated sodium has glowed orange up till now, who is to say itwill not start glowing blue sometime in the next century?
In this respect induction contrasts with deduction. In deductive inferences the premises guarantee the conclusion. For example, if you know that Either thissubstance is sodium or it is potassium, and then learn further that It is not sodium , you can conclude with certainty that It is potassium. The truth of the premises leaves no room for the conclusion to be anything but true. But in an inductive inference this does not hold. To take the simplest case, if you are told,for properties A and B. that Each of the As observed so far has been B. this does not guarantee that All As, includingfuture ones, are Bs. It is perfectly possible that the former claim may be true, but the latter false.
The problem of induction seems to pose a threat to all scientific knowledge. All scientific discoveries worth their name are in the form of general principles. Galileo's law of free fall says that 'All bodies fall with constant acceleration'; Newton's law of gravitation says that 'All bodies attract each other in proportion to their masses and in inverse proportion to the square of the distance between them'; Avogadro's law says that 'All gases at the same temperature and pressure contain the same number of molecules per unit volume'; and so on. The problem of induction calls the authority of all these laws in question. For if our evidence is simply that these laws have worked so far, then how can we be sure that they will not be disproved by future occurrences?
Many issues in the metaphysics of science hinge on the notion of causation. This notion is as important in science as it is in everyday thinking, and much scientific theorizing is concerned specifically to identify the causes of various phenomena. However, there is little philosophical agreement on what it means to say that one event is the cause of another.
Modern discussion of causation starts with David Hume, who argued that causation is simply a matter of CONSTANT CONJUNCTION . According to Hume, one event causes another if and only if events of the type to which the first event belongs regularlyoccur in conjunction with events of the type to which the second event belongs. This formulation, however, leaves a number of questions open. Firstly, there is the problem of distinguishing genuinecausal laws from accidental regularities. Not all regularities are sufficiently lawlike to underpin causal relationships. Being a screw in my desk could well be constantly conjoined with being made of copper, without its being true that these screws are made of copper because they are in my desk. Secondly, the idea ofconstant conjunction does not give a direction to causation. Causes need to be distinguished from effects. But knowing that A-type events are constantly conjoined with B-type events does not tell us which of A and B is the cause and which the effect, since constant conjunction is itself a symmetric relation. Thirdly, there is a problem about probabilistic causation. When we say that causes and effects are constantly conjoined, do we mean that the effects are always found with the causes, or is it enough that the causes make the effects probable?
Many philosophers of science this century have preferred to talk aboutexplanation rather than causation. According to the covering-law model of explanation, something is explained if it can be deduced from premises which include one or more laws. As applied to the explanation of particular events, this implies that one particular event can be explained if it is linked by a law to some other particular event. However, while they are often treated as separate theories, the covering-law account of explanation is at bottom little more than a variant of Hume's constant conjunction account of causation. This affinity shows up in the fact that the covering-law account faces essentially the same difficulties as Hume: (1) in appealing to deductions from 'laws', it needs to explain the difference between genuine laws and accidentally true regularities; (2) it omits the requisite directionality, in that it does not tell us why we should not 'explain' causes by effects, as well as effects by causes; after all, it is as easy to deduce the height of a flagpole from the length of its shadow and the laws of optics, as to deduce the length of the shadow from the height of the pole and the same laws;(3) are the laws invoked in explanation required to be exceptionless and deterministic, or is it acceptable, say, to appeal to the merely probabilistic fact that smoking makes cancer more likely, in explaining why some particular person developed cancer?
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