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Home , Realism, Scientific realism

Chapter 4 Scientific and anti-realism Like most philosophical 'isms', comes in many Realism and anti-realism different versions, so cannot be defined in a totally precise way. But the basic is straightforward. Realists hold that the aim of is to provide a true description ofthe world. This may sound like a fairly innocuous doctrine. For surely no-one thinks science is aiming to produce a false description ofthe world. But that is not what anti-realists think. Rather, anti-realists hold that the aim of science is to provide a true description ofa certain part ofthe world - the 'observable' part. As far as the '' part of the world goes, it makes no odds whether what science says is true There is a very ancient debate in between two or not, according to anti-realists. opposing schools ofthought called realism and . Realism holds that the physical world exists independently ofhuman What exactly do anti-realists mean by the observable part ofthe and . Idealism denies this - it claims that the world? They mean the everyday world oftables and chairs, trees physical world is in some way dependent on the conscious activity and animals, test-tubes and Bunsen burners, thunderstorms and ofhumans. To most people, realism seems more plausible than snow showers, and so on. Things such as these can be directly idealism. For realism fits well with the common-sense view that perceived by human - that is what it means to call them the about the world are 'out there' waiting to be discovered observable. Some branches ofscience deal exclusively with objects by us, but idealism does not. Indeed, at first glance idealism can that are observable. An example is palaeontology, or the study of sound plain silly. Since rocks and trees would presumably contin"lle fossils. Fossils are readily observable - anyone with normally to exist even ifthe human race died out, in what sense is their functioning eyesight can see them. But other make claims dependent on human ? In , the issue is a bit about the unobservable region ofreality. Physics is the obvious more subtle than this, and continues to be discussed by example. Physicists advance about , electrons, philosophers today. quarks, leptons, and other strange particles, none ofwhich can be observed in the normal sense ofthe word. Entities ofthis sort lie Though the traditional realism/idealism issue belongs to an area of beyond the reach ofthe observational powers ofhumans. philosophy called , it has actually got nothing in particular to do with science. Our concern in this chapter is with a With respect to sciences like palaeontology, realists and anti-realists more modern debate that is specifically about science, and is in do not disagree. Since fossils are observable, the realist thesis that some ways analogous to the traditional issue. The debate is between science aims to truly describe the world and the anti-realist thesis a position known as scientific realism and its converse, known as that science aims to truly describe the observable world obviously anti-realism or . From now on, we shall use the coincide, as far as the study offossils is concerned. But when it word 'realism' to mean scientific realism, and 'realist' to mean comes to sciences like physics, realists and anti-realists disagree. scientific, realist. Realists say that when physicists put forward theories about

58 59 --- electrons and quarks, they are trying to provide a true description of attempted descriptions ofreality; anti-realists think this the subatomic world, just as paleontologists are trying to provide a interpretation is inappropriate for theories that talk about true description ofthe world offossils. Anti-realists disagree: they unobservable entities and processes. While it would certainly be see a fundamental between theories in subatomic physics interesting to discover scientists' own views on the realism/anti­ and in palaeontology. realism debate, the issue is ultimately a philosophical one.

What do anti-realists think physicists aTe up to when they talk Much ofthe motivation for anti-realism stems from the beliefthat about unobservable entities? Typically they claim that these entities we cannot actually attain ofthe unobservable part of are merely convenient fictions, introduced by physicists in order to - it lies beyond human ken. On this view, the limits to help predict observable phenomena. To illustrate, consider the scientific knowledge are set by our powers ofobservation. So kinetic ofgases, which says that any volume ofa gas contains science can give us knowledge offossils, trees, and sugar crystals, a large number ofvery small entities in . These entities ­ but not ofatoms, electrons, and quarks - for the latter are molecules - are unobservable. From the kinetic theory we can unobservable. This view is not altogether implausible. For no-one deduce various consequences about the observable behaviour of could seriously doubt the existence offossils and trees, but the same gases, e.g. that heating a sample ofgas cause it to expand ifthe is not true ofatoms and electrons. As we saw in the last chapter, in i pressure remains constant, which can be verified experimentally. the late 19th century many leading scientists did doubt the Z ;X According to anti-realists, the only purpose ofpositing existence ofatoms. Anyone who accepts such a view must obviously ;- II <; unobservable entities in the kinetic theory is to deduce give some explanation ofwhy scientists advance theories about i II t consequences ofthis sort. Whether or not gases really do contain unobservable entities, ifscientific knowledge is limited to what can ! ; I - mo ecules in motion doesn't ; the point ofthe kinetic theory be observed. The explanation anti-realists give is that they are i if is not to truly describe the hidden facts, butjust to provide a convenient fictions, designed to help predict the behaviour ofthings 3 convenient way ofpredicting . We can see why anti-"lt in the observable world. realism is sometimes called 'instrumentalism' - it regards scientific theories as instruments for helping us predict observational Realists do not agree that scientific knowledge is limited by our phenomena, rather than as attempts to describe the underlying powers ofobservation. On the contrary, they believe we already ofreality. have substantial knowledge ofunobservable reality. For there is every reason to believe that our best scientific theories are true, and Since the realism/anti-realism debate concerns the aim ofscience, our best scientific theories talk about unobservable entities. one might think it could be resolved by simply asking the scientists Consider, for example, the atomic theory ofmatter, which says that themselves. Why not do a straw poll ofscientists asking them about all matter is made up ofatoms. The atomic theory is capable of their aims? But this suggestion misses the point - it takes the explaining a great range offacts about the world. According to expression 'the aim ofscience' too literally. When we ask what the realists, that is good evidence that the theory is true, Le. that matter aim ofscience is, we are not asking about the aims ofindividual really is made up ofatoms that behave as the theory says. Ofcourse scientists. Rather, we are asking how best to make sense ofwhat the dreory might be false, despite the apparent evidence in its scientists say and do - how to interpret the scientific enterprise. favour, but so might any theory. Just because atoms are Realists think we should interpret all scientific theories as unobservable, that is no reason to interpret atomic theory as

60 61 anything other than an attempted description ofreality - and a very The empirical success oftheories that posit unobservable entities is successful one, in all likelihood. the basis ofone ofthe strongest arguments for scientific realism, called the 'no miracles' argument. According to this argument, it Strictly we should distinguish two sorts ofanti-realism. According would be an extraordinary coincidence ifa theory that talks about to the first sort, talk ofunobservable entities is not to be understood electrons and atoms made accurate about the literally at all. So when a scientist puts forward a theory about observable world - unless electrons and atoms actually exist. If electrons, for example, we should not take him to be asserting the there are no atoms and electrons, what explains the theory's close fit existence ofentities called 'electrons'. Rather, his talk ofelectrons is with the observational data? Similarly, how do we explain the metaphorical. This form ofanti-realism was popular in the first half technological advances our theories have led to, unless by supposing ofthe 20th century, but few people advocate it today. It was that the theories in question are true? Ifatoms and electrons are motivated largely by a doctrine in the philosophy oflanguage, just 'convenient fictions', as anti-realists maintain, then why do according to which it is not possible to make meaningful assertions lasers work? On this view, an anti-realist is akin to believing about things that cannot in be observed, a doctrine that in miracles. Since it is obviously better not to believe in miracles if a few contemporary philosophers accept. The second sort ofanti­ non-miraculous alternative is available, we should be realists not realism accepts that talk ofunobservable entities should be taken at anti-realists. 1l face : ifa theory says that electrons are negatively charged, it is f ! true ifelectrons do exist and are negatively charged, but false This argument is not intended to prove that realism is right and f ~ 'l:i otherwise. But we will never know which, says the anti-realist. So anti-realism wrong. Rather it is a plausibility argument - an :- .: the correct attitude towards the claims that scientists make about to the best explanation. The phenomenon to be explained a _! unobservable reality is one oftotal agnosticism. They are either true is the fact that many theories that postulate unobservable entities i f or false, but we are incapable offinding out which. Most modern enjoy a high level ofempirical success. The best explanation ofthis f anti-realism is ofthis second sort. .,{" fact, say advocates ofthe 'no miracles' argument, is that the theories are true - the entities in question really exist, and behave just as the theories say. Unless we accept this explanation, the empirical The 'no miracles' argument success ofour theories is an unexplained mystery. Many theories that posit unobservable entities are empirically successful - they make excellent predictions about the behaviour of Anti-realists have responded to the 'no miracles' argument in objects in the observable world. The kinetic theory ofgases, various ways. One response appeals to certain facts about the mentioned above, is one example, and there are many others. history ofscience. Historically, there are many cases oftheories that Furthermore, such theories often have important technological we now believe to be false but that were empirically quite successful applications. For example, laser technology is based on a theory in their day. In a well-known article, the American philosopher of about what happens when electrons in an go from higher to science lists more than 30 such theories, drawn from lower energy-states. And lasers work - they allow us to correct our a range ofdifferent scientific disciplines and eras. The phlogiston vision, attack our enemies with guided missiles, and do much more theory ofcombustion is one example. This theory, which was widely besides. The theory that underpins laser technology is therefore accepted until the end ofthe 18th century, held that when any highly empirically successful. burns it releases a substance called 'phlogiston' into the

62 63 -- atmosphere. Modern chemistry teaches us that this is false: there is find historical examples ofempirically successful theories that later no such substance as phlogiston. Rather, burning occurs when turned out to be false. things react with oxygen in the air. But despite the non-existence ofphlogiston, the phlogiston theory was empirically quite Whether these refinements can really save the 'no miracles' successful: it fitted the observational data available at the argument is debatable. They certainly reduce the number of reasonably well. historical counter-examples, but not to zero. One that remains is the wave theory oflight, first put forward by Christian Huygens in Examples ofthis sort suggest that the 'no miracles' argument for 1690. According to this theory, light consists ofwave-like vibrations scientific realism is a bit too quick. Proponents ofthat argument in an invisible medium called the ether, which was supposed to regard the empirical success oftoday's scientific theories as permeate the whole universe. (The rival to the wave theory was the evidence oftheir . But the history ofscience shows that particle theory oflight, favoured by Newton, which held that light empirically successful theories have often turned out to be false. So consists ofvery small particles emitted by the light source.) The how do we know that the same fate will not befall today's theories? wave theory was not widely accepted until the French physicist How do we know that the atomic theory ofmatter, for example, will Auguste Fresnel formulated a mathematical version ofthe theory in not go the same way as the phlogiston theory? Once we pay due 1815, and used it to predict some surprising new optical .. attention to the history ofscience, argue the anti-realists, we see phenomena. Optical experiments confirmed Fresnel's predictions, I that the inference from empirical success to theoretical truth is a convincing many 19th-century scientists that the wave theory of OS very shaky one. The rational attitude towards the atomic theory is light must be true. But modern physics tells us the theory is not "'_i thus one ofagnosticism - it may be true, or it may not. We just do true: there is no such thing as the ether, so light doesn't consist of not know, say the anti-realists. vibrations in it. Again, we have an example ofa false but empirically f successful theory. This is a powerful counter to the 'no miracles' argument, but it it! not completely decisive. Some realists have responded by modifYing The important feature ofthis example is that it tells against even the argument slightly. According to the modified version, the the modified version ofthe 'no miracles' argument. For Fresnel's empirical success ofa theory is evidence that what the theory says theory did make novel predictions, so qualifies as empirically about the unobservable world is approximately true, rather than successful even relative to the stricter ofempirical success. precisely true. This weaker claim is less vulnerable to counter­ And it is hard to see how Fresnel's theory can be called examples from the history ofscience. It is also more modest: it 'approximately true', given that it was based around the idea ofthe allows the realist to admit that today's theories may not be correct ether, which does not exist. Whatever exactly it means for a theory down to every last detail, while still holding that they are broadly on to be approximately true, a necessary condition is surely that the the right lines. Another way ofmodifYing the argument is by entities the theory talks about really do exist. In short, Fresnel's refining the notion ofempirical success. Some realists hold that theory was empirically successful even according to a strict empirical success is not just a matter offitting the known understanding ofthis notion, but was not even approximately true. observational data, but rather allowing us to predict new The moral ofthe story, say anti-realists, is that we should not observational phenomena that were previously unknown. Relative assume that modern scientific theories are even roughly on the right to this more stringent criterion ofempirical success, it is less easy to lines, just because they are so empirically successful.

64 65 ~

Whether the 'no miracles' argument is a good argument for One such problem concerns the relation between and scientific realism is therefore an open question. On the one hand, detection. Entities such as electrons are obviously not observable in the argument is open to quite serious objections, as we have seen. the ordinary sense, but their presence can be detected using special On the other hand, there is something intuitively compelling about pieces ofapparatus called particle detectors. The simplest particle the argument. It really is hard to accept that atoms and electrons detector is the cloud chamber, which consists ofa closed container might not exist, when one considers the amazing success oftheories filled with air that has been saturated with water-vapour (Figure 9). that postulate these entities. But as the history ofscience shows, we When charged particles such as electrons pass through the should be very cautious about assuming that our current scientific chamber, they collide with neutral atoms in the air, converting them theories are true, however well they fit the data. Many people have into ions; water vapour condenses around these ions causing liquid assumed that in the past and been proved wrong. droplets to form, which can be seen with the naked eye. We can follow the path ofan electron through the cloud chamber by watching the tracks ofthese liquid droplets. Does this mean that The observable/unobservable distinction electrons can be observed after all? Most philosophers would say Central to the debate between realism and anti-realism is the no: cloud chambers allow us to detect electrons, not observe them distinction between things that are observable and things that directly. In much the same way, high-speed jets can be detected by 11 are not. So far we have simply taken this distinction for granted ­ the vapour trails they leave behind, but watching these trails is not Z ; i ;X tables and chairs are observable, atoms and electrons are not. But in observing the jet. But is it always clear how to distinguish observing : o fact the distinction is quite philosophically problematic. Indeed, from detecting? Ifnot, then the anti-realist position could be i l' .. ... one ofthe main arguments for scientific realism says that it is not in trouble. a j possible to draw the observable/unobservable distinction in a i f principled way. In a well-known defence ofscientific realism from the early 1960s, ;' '''t the American philosopher Grover Maxwell posed the following Why should this be an argument for scientific realism? Because the problem for the anti-realist. Consider the following sequence of coherence ofanti-realism is crucially dependent on there being a events: looking at something with the naked eye, looking at clear distinction between the observable and the unobservable. something through a window, looking at something through a pair Recall that anti-realists advocate a different attitude towards ofstrong glasses, looking at something through binoculars, looking scientific claims, depending on whether they are about observable at something though a low-powered microscope, looking at or unobservable parts ofreality - we should remain agnostic about something through a high-powered microscope, and so on. Maxwell the truth ofthe latter, but not the former. Anti-realism thus argued that these events lie on a smooth continuum. So how do we presupposes that we can divide scientific claims into two sorts: decide which count as observing and which not? Can a biologist those that are about observable entities and processes, and those observe micro-organisms with his high-powered microscope, or can that are not. Ifit turns out that this division cannot be made in a he only detect their presence in the way that a physicist can detect satisfactory way, then anti-realism is obviously in serious trouble, the presence ofelectrons in a cloud chamber? Ifsomething can only and realism wins by default. That is why scientific realists are often be seen with the help ofsophisticated scientific instruments, does it keen to emphasize the problems associated with the observable/ count as observable or unobservable? How sophisticated can the unobservable distinction. instrumentation be, before we have a case ofdetecting rather

66 67 than observing? There is no principled way ofanswering these questions, Maxwell argued, so the anti-realist's attempt to classifY entities as either observable or unobservable is doomed to failure.

Maxwell's argument is bolstered by the fact that scientists themselves sometimes talk about 'observing' particles with the help ofsophisticated bits ofapparatus. In the philosophical literature, electrons are usually taken as examples ofunobservable entities, but scientists are often perfectly happy to talk about 'observing' electrons using particle detectors. Ofcourse, this does not prove that the philosophers are wrong and that electrons are observable after all, for the scientists' talk is probably best regarded as aJat;on-de-parZer. Similarly, the fact that scientists talk about having 'experimental proof ofa theory does not mean that experiments can really prove theories to be true, as we saw in Chapter 2. Nonetheless, ifthere really is a philosophically important observable/unobservable distinction, as anti-realists maintain, it is odd that it corresponds so badly with the way scientists themselves speak.

Maxwell's arguments are powerful, but by no means completely decisive. , a leading contemporary anti-realist, claims that Maxwell's arguments only show 'observable' to be a vague . A vague concept is one that has borderline cases ­ cases that neither clearly do nor clearly do not fall under it. 'Bald' is an obvious example. Since hair loss comes in degrees, there are many men ofwhom it's hard to say whether they are bald or not. But van Fraassen points out that vague are perfectly 9. One ofthe first photographs to show the tracks ofsubatomic usable, and can mark genuine distinctions in the world. (In fact, particles in a cloud chamber. The picture was taken by the cloud most concepts are vague to at least some extent.) No-one would chamber's inventor, English physicist C. T. R. Wilson, at the Cavendish argue that the distinction between bald and hirsute men is unreal or Laboratory in Cambridge in 1911. The tracks are due to alpha particles emitted by a small amount ofradium on the top ofa metal tongue unimportant simply because 'bald' is vague. Certainly, ifwe attempt inserted into the cloud chamber. As an electrically charged particle to draw a sharp dividing line between bald and hirsute men, it will moves through the water vapour in a cloud chamber, it ionizes the gas, arbitrary. But since there are clear-cut cases ofmen who are bald and water drops condense on the ions, thus producing a track of droplets where the particle has passed. and clear-cut cases ofmen who are not, the impossibility of ~lrawing

69 a sharp dividing line doesn't matter. The concept is perfectly usable The argument despite its vagueness. One argument for anti-realism centres on the relationship between Precisely the same applies to 'observable', according to van scientists' observational data and their theoretical claims. Anti- Fraassen. There are clear-cut cases ofentities that can be observed, realists emphasize that the ultimate data to which scientific theories for example chairs, and clear-cut cases ofentities that cannot, for are responsible is always observational in character. (Many realists example electrons. Maxwell's argument highlights the fact that would agree with this claim.) To illustrate, consider again the there are also borderline cases, where we are unsure whether the kinetic theory ofgases, which says that any sample ofgas consists of entities in question can be observed or only detected. So ifwe try to molecules in motion. Since these molecules are unobservable, we draw a sharp dividing line between observable and unobservable obviously cannot test the theory by directly observing various entities, it will inevitably be somewhat arbitrary. But as with samples ofgas. Rather, we need to deduce from the theory some baldness, this does not show that the observable/unobservable statement that can be directly tested, which will invariably be about distinction is somehow unreal or unimportant, for there are clear­ observable entities. As we saw, the kinetic theory implies that a cut cases on either side. So the vagueness ofthe term 'observable' is sample ofgas will expand when heated, ifthe pressure remains no embarrassment to the anti-realist, van Fraassen argues. It only constant. This statement can be directly tested, by observing the ~ sets an upper limit on the precision with which she can formulate readings on the relevant pieces ofapparatus in a laboratory (Figure Z ~ her position. 10). This example illustrates a general truth: observational data ;' II 11 ~ >- II How strong an argument is this? Van Fraassen is certainly right that ~ 1 the existence ofborderline cases, and the consequent impossibility i f ofdrawing a sharp boundary without arbitrariness, does not show ;' the observable/unobservable distinction to be unreal. To that .~ extent, his argument against Maxwell succeeds. However, it is one thing to showthat there is a real distinction between observable and unobservable entities, and another to show that the distinction is capable ofbearing the philosophical weight that anti-realists wish to place on it. Recall that anti-realists advocate an attitude of complete agnosticism towards claims about the unobservable part ofreality - we have no way ofknowing whether they are true or not, they say. Even ifwe grant van Fraassen his point that there are clear cases ofunobservable entities, and that that is enough for the anti­ realist to be getting on with, the anti-realist still needs to provide an argument for thinking that knowledge ofunobservable reality is impossible. 10. DiaIatometerfor measuring the change in volume ofa gas as its temperature varies.

70 71 constitute the ultimate evidence for claims about unobservable argument by insisting that this claim is true only in a trivial and entities. uninteresting sense. In principle, there will always be more than one possible explanation ofa given set ofobservations. But, say the Anti-realists then argue that the observational data realists, it does not follow that all ofthese possible explanations are 'underdetermine' the theories scientists put forward on their basis. as good as one another. Just because two theories can both account What does this mean? It means that the data can in principle be for our observational data does not mean that there is nothing to explained by many different, mutually incompatible, theories. In choose between them. For one ofthe theories might be simpler than the case ofthe kinetic theory, anti-realists will say that one possible the other, for example, or might explain the data in a more explanation ofthe observational data is that gases contain large intuitively plausible way, or might postulate fewer hidden causes, numbers ofmolecules in motion, as the kinetic theory says. But they and so on. Once we acknowledge that there are criteria for theory will insist that there are other possible explanations too, which in addition to compatibility with the observational data, the conflict with the kinetic theory. So according to anti-realists, problem ofunderdetermination disappears. Not all the possible scientific theories that posit unobservable entities are explanations ofour observational data are as good as one another. underdetermined by the observational data - there will always be a Even ifthe data that the kinetic theory explains can in principle be number ofcompeting theories that can account for that data explained by alternative theories, it does not follow that these ~ equally well. alternatives can explain as well as the kinetic theory does. .!! oX 'S It is easy to see why the underdetermination argument supports an This response to the underdetermination argument is bolstered by ~ _... anti-realist view ofscience. For iftheories are always the fact that there are relatively few real cases of s underdetermined by the observational data, how can we ever have underdetermination in the history ofscience. Ifthe observational f reason to believe that a particulartheory is true? Suppose a scientist data can always be explained equally well by many different advocates a given theory about unobservable entities, on the 't theories, as anti-realists maintain, surely we should expect to find grounds that it can explain a large range ofobservational data. An scientists in near perpetual disagreement with one another? But anti-realist philosopher ofscience comes along, and argues that the that is not what we find. Indeed, when we inspect the historical data can in fact be accounted for by various alternative theories. If record, the situation is almost exactly the reverse ofwhat the the anti-realist is correct, it follows that the scientist's confidence in underdetermination argument would lead us to expect. Far from her theory is misplaced. For what reason does the scientist have to scientists being faced with a large number ofalternative choose the theory she does, rather than one ofthe alternatives? In explanations oftheir observational data, they often have difficulty such a situation, surely the scientist should admit that she has no finding even one theory that fits the data adequately. This lends idea which theory is true? Underdetermination leads naturally to support to the realist view that underdetermination is merely a the anti-realist conclusion that agnosticism is the correct attitude to philosopher's worry, with little relation to actual scientific practice. take towards claims about the unobservable region ofreality. Anti-realists are unlikely to be impressed by this response. After all, But is it actually true that a given set ofobservational data can philosophical worries are still genuine ones, even iftheir practical always be explained by many different theories, as anti-realists implications are few. Philosophy may not change the world, butthat maintain? Realists usually respond to the underdetermination doesn't mean it isn't important. And the suggestion that criteria

72 73 such as simplicity can be used to adjudicate between competing He cites various pieces ofobservational data to support this theories immediately invites the awkward question ofwhy simpler hypothesis, e.g. that satellite pictures ofthe moon show a large theories should be thought more likely to be true; we touched on crater that wasn't there before 1987. However, this data can in this issue in Chapter 2. Anti-realists typically grant that the principle be explained by many alternative hypotheses - perhaps a problem ofunderdetermination can be eliminated in practice by volcanic eruption caused the crater, or an earthquake. Or perhaps using criteria such as simplicity to discriminate between competing the camerathat took the satellite pictures was faulty, and there is no explanations ofour observational data. But they deny that such crater at all. So the scientist's hypothesis is underdetermined by the criteria are reliable indicators ofthe truth. Simpler theories may be data, even though the hypothesis is about a perfectly observable more convenient to work with, but they are not intrinsically more event - a meteorite striking the moon. Ifwe apply the probable than complex ones. So the underdetermination argument underdetermination argument consistently, say realists, we are stands: there are always multiple explanations ofour data, we have forced to conclude that we can only acquire knowledge ofthings no way ofknowing which is true, so knowledge ofunobservable that have actually been observed. reality cannot be had. This conclusion is very implausible, and is not one that any However, the story does not end here; there is a further realist philosopher ofscience would wish to accept. For much ofwhat l!l comeback. Realists accuse anti-realists ofapplying the scientists tell us concerns things that have not been observed ­ ; ;X underdetermination argument selectively. Ifthe argument is think ofice ages, , continental drift, and the like. To say o applied consistently, it rules out not only knowledge ofthe that knowledge ofthe unobserved is impossible is to say that most i: unobservable world, but also knowledge ofmuch ofthe observable ofwhat passes for scientific knowledge is not really knowledge at j world, say the realists. To understand why realists say this, notice all. Ofcourse, scientific realists do not accept this conclusion. if that many things that are observable never actually get observed. Rather, they take it as evidence that the underdetermination For example, the vast majority ofliving organisms on the planef"! argument must be wrong. Since science clearly does give us never get observed by humans, but they are clearly observable. Or knowledge ofthe unobserved, despite the fact that theories about think ofan event such as a large meteorite hitting the earth. No-one the unobserved are underdetermined by our data, it follows that has ever witnessed such an event, but it is clearly observable. Itjust underdetermination is no barrier to knowledge. So the fact that our so happens that no human was ever in the right place at the right theories about the unobservable are also underdetermined by our time. Only a small fraction ofwhat is observable actually gets data does not mean that science cannot give us knowledge ofthe observed. unobservable region ofthe world.

The key point is this. Anti-realists claim that the unobservable part In effect, realists who argue this way are saying that the problem ofreality lies beyond the limits ofscientific knowledge. So they raised by the underdetermination argument is simply a allow that we can have knowledge ofobjects and events that are sophisticated version ofthe problem ofinduction. To say that a observable but unobserved. But theories about unobserved objects theory is underdetermined by the data is to say that there are and events are just as underdetermined by our data as are theories alternative theories that can account for the same data. But this is about unobservable ones. For example, suppose a scientist puts effectively just to say that the data do not entail the theory: the forward the hypothesis that a meteorite struck the moon in 1987. inference from the data to the theory is non-deductive. Whether the

74 75 theory is about unobservable entities, or about observable but Chapter 5 unobserved entities, makes no difference - the ofthe situation is the same in both cases. Ofcourse, showing that the underdetermination argument is just a version ofthe problem of Scientific change and induction does not mean that it can be ignored. For there is little consensus on how the problem ofinduction should be tackled, as scientific revolutions we saw in Chapter 2. But it does mean that there is no special difficulty about unobservable entities. Therefore the anti-realist position is ultimately arbitrary, say the realists. Whatever problems there are in understanding how science can give us knowledge of atoms and electrons are equally problems for understanding how science can give us knowledge ofordinary, medium-sized objects. Scientific change fast. Pick virtually any scientific discipline you like, and you can be sure that the prevalent theories in that discipline will be very different from those of50 years ago, and extremely different from those of100 years ago. Compared with other areas ofintellectual endeavour such as philosophy and the arts, science is a rapidly changing activity. A number ofinteresting philosophical questions centre on the issue of scientific change. Is there a discernible to the way scientific ideas change over time? When scientists abandon their existing theory in favour ofa new one, how should we explain this? Are later scientific theories objectively better than earlier ones? Or does the concept ofobjectivity make sense at all?

Most modern discussion ofthese questions takes offfrom the work ofthe late , an American historian and philosopher of science. In 1963 Kuhn published a book called The Structure of Scientific Revolutions, unquestionably the most influential work of philosophy ofscience in the last 50 years. The impact ofKuhn's ideas has also been felt in other academic disciplines such as sociology and anthropology, and in the general intellectual culture at large. (The Guardian newspaper included The Structure of Scientific Revolutions in its list ofthe 100 most influential books of the 20th century.) In order to understand why Kuhn's ideas caused

76 77 22/0 ~5 '(: ~ \ {I', e Available soon: \<'::::. 1'/:- L THE TUDORS johnGuy FUNDAMENTALISM TWENTI ETH-CENTU RY Malise Ruthven BRITAIN KennethO.Morgan HABERMAS Gordon Finlayson WITIGENSTEIN A. C. Grayling HIEROGLYPHS WORLD MUSIC Philip Bohlman Penelope Wilson AFRICAN HISTORY HIROSHIMA B. R. Tomlinson john Parker and Richard Rathbone HUMAN EVOLUTION ANCI ENT EGYPT Ian Shaw Bernard Wood TH E BRA IN Michael O'Shea INTERNATIONAL BUDDHIST Paul Wilkinson Damien Keown JAZZ Brian Morton CHAOS Leonard Smith MANDELA Tom Lodge CHRISTIANITY LindaWoodhead MEDICAL ETHICS CITIZENSHIP Richard Bellamy Tony Hope CLASSICAL ARCH ITECTU RE THE Martin Davies Robert Tavernor MYTH Robert Segal Samir Okasha CLON ING Arlene judith Klotzko NATIONALISM Steven Grosby CONTEMPORARY ART PERCEPTION Richard Gregory Julian Stallabrass PHILOSOPHYOF RELIGION PH ILOSOPHY TH ECRUSADES jack Copeland and Diane Proudfoot ­ Christopher Tyerman PHOTOGRAPHY Steve Edwards DE RRI DA Simon Glendinning TH E RAJ Denis Judd OF SCI ENCE DESIGN john Heskett THE RENAISSANCE DINOSAURS David Norman jerry Bratton ~~J. DREAMI NG J. Allan Hobson RENAISSANCE ART ake>- A Very Short Introduction ECONOMICS Partha Dasgupta Geraldine johnson THEENDOFTHEWORLD SARTRE Christina Howells 14046 Bill McGuire THE SPANISH CIVIL WAR Thomas Flynn Helen Graham TH E FI RST WORLD WAR TRAG EDY Adrian Poole Michael Howard TH ETWENTI ETH CENTURY FREE WI LL Thomas Pink Martin Conway

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