Thursday, 5 June 2014

Nancy Cartwright on Scientific Laws

Cartwright on Non-Modalised and Non-Universalised Scientific Laws

Nancy Cartwright doesn’t believe that there are ‘modalised universal or probabilistic generalisations’ (201):

I think there are no descriptive laws in the sense of modalised universal or probabilistic generalisations – there are none of those which are not ceteris paribus. I don’t think it follows from that there are no true nomological type statements in physics. When you ascribe a capacity to an electron, because of its charge, to repel other electrons or attract protons, I think that capacity-ascription is universal and it’s true. But I think it in no way can be translated into a modalised universal generalisation. It has to be seen as a capacity statement which works in a very different way than one of these laws as traditionally conceived. (201)

I think it is a very radical position to say that there are no ‘modalised universal or probabilistic generalisations – there are none of those which are not ceteris paribus’ (201) in physics or any of the other natural sciences. That means that no law of physics is necessary or necessarily true. Of course, ‘probabilistic generalisations’ by definition cannot be necessary or necessarily true. All these generalisations (or laws) will contain ceteris paribus ‘escape clauses’ which will say that they only hold if so-and-so or this-and-that is the case or if ‘all things remain equal’. This must mean that all things never remain equal. That is, there are always some ceteris paribus amendments of some kind thus the generalisation (or law) can never be ‘modalised’. However, Cartwright goes on to say something which appears, prima facie, to go against what she says in the first sentence. She says that there are ‘true nomological type statements in physics’ (201). That must mean that ‘nomological’ is not a modal term. That is, something can be ‘law-like’, or even a law, without it being necessary (or even probable?). We can have laws of physics without them being necessary or even universal in nature. This seems to go against not only scientific and philosophical conceptions of natural laws, but even what the layperson believes.

Cartwright, instead, talks in terms of the ‘capacities’ or natural phenomena like, in her example, electrons. This may well be a ‘dispositional’ analysis of causation or of natural phenomena. If it is about the ‘capacity’ of, say, an electron to do this or that, then this analysis must also be counterfactual in nature in that it is not telling us what the electron is doing, but what it would do given such-and-such circumstances. More specifically, the electron has the capacity, or contains the disposition, "to repel other electrons or attract protons" (201). Again, this does not means that a particular electron, or even all electrons, are repelling other electrons or attracting protons, only that they would do so given such-and-such a situation. Is this necessarily the case? Is it highly probable or probable at all? However, despite the fact that Cartwright said that that there are no "modalised universal or probabilistic generalisations’ she now says that ‘capacity-ascription is universal and it’s true" (201). This appears to go against her earlier statement, as just expressed. However, perhaps the universality of the ‘capacity-ascription’ is itself counterfactual in nature in that it is not universal as it stands; though it would be universal given such-and-such a situation or set of conditions. This may simply mean that at no single moment in time is every electron either repelling other electrons or attracting protons but that each and every one of them would do so given such-and-such conditions. That is, even though a single or even all electrons are not at this moment repelling other electrons or attracting protons they would do given such-and-such conditions – that is, perhaps, if they were contiguous with other electrons or with protons.

So it is no surprise that she still says that this ‘capacity-ascription’ can ‘in no way be translated into a modalised universal generalisation’ (201). Because of this dispositional analysis of electrons, we can say that because it is the case the every electron is not repelling other electrons or attracting protons at this or any moment in time, then we cannot state universal generalisations about electrons or say that each or every electron must be necessarily behaving in such-and-such a way. It may even be the case that no electron is the universe is either repelling other electrons or attracting protons. This will certainly be the case when it comes to individual electrons and their behaviour. It is not surprising, therefore, that this seemingly counterfactual analysis of laws or of electrons "works in a very different way than one of these laws as traditionally conceived" (201).

In conclusion, this account of causation and natural law seems to tally very well with Hume’s empiricist account. Hume is still seen to be of vital importance when it comes to these issues in the philosophy of science and even in science itself.

To conclude. Cartwright still accepts the nomological reality of natural laws and scientific generalisations and even concludes herself by saying that "the planetary system is a nomological machine" (201). That is, everything about the planetary system is ‘law-like’ and works according to the laws of physics; though none of these laws are modal or necessary in nature and we can’t offer any true universal generalisations about them unless they contain ceteris paribus amendments which, of course, effectively render them non-universal or counterfactual in nature.

Cartwright on Capacity-Ascriptions

Nancy Cartwright goes into more detail as to why she offers a dispositional or ‘capacity-ascription’ counterfactual analysis of scientific law or causation:

I think most cases of causation are cases of interaction and that they’re not intelligible in a scientific way. That is, not much of what happens in the natural world is governed in a systematic way, that it takes an enormous amount of effort in special background conditions in special circumstances before you get regular repeatable behaviour. The more standard view is that everything that happens is an instance of some regularity, albeit a very complicated or a very abstract one which we may never know. And since I think it’s very difficult to get regularities at all, they’re not just lying around and everything that happens is an instance of them, then I genuinely believe that most things that happen in the world can’t be subsumed under a regularity, or ought to be subsumed under a regularity. A lot of what happens simply is a result of interaction which we can’t have a handle on. (202)

This dispositional or counterfactual analysis really does go against the standard account of causation and scientific law. We still have causation, or even regularity, though "most cases of causation are cases of interaction and that they’re not intelligible in a scientific way" (202). So instead of talking about ‘causation’ at all perhaps we should talk about simple ‘interaction’, as Cartwright does. The other way of putting this is to say, as Cartwright does, that "not much of what happens in the natural world is governed in a systematic way" (202). This too goes against traditional conceptions of science. Not only against the Newtonian idea of the systematicity of nature, but even of its very intelligibility. If one does not have systematicity, or even regularity, then this will make the natural world a lot more difficult to understand because the application of laws will be all the more limited and complex (if not particular). In order to get regularity and systematicity "it takes an enormous amount of effort in special background conditions in special circumstances before you get regular repeatable behaviour" (202). If one does in the end ‘find’ regularity and the instantiation of natural law, they come at the cost of much analysis of "special background conditions in special circumstances". That is, the ceteris paribus list will be large and complex. And if some cases of regularity are "very complicated or very abstract one which we may never know" (202) one can apply anti-realist arguments to such a fact by saying that an unknowable regularity, one that is even unknowable in principle, is not an example or a case of regularity at all! That is, if we cannot fathom a regularity, how then do we know that it must be a regularity in the first place if we have no evidence for it or no means of knowing that it is in fact some kind of regularity? Cartwright does not say that ‘most things’ cannot be subsumed under a natural law, but that ‘most things’ cannot even ‘be subsumed under a regularity’ (202). Not only that: it is not even the case, in all instances, that they "ought to be subsumed under a regularity" (202). Perhaps subsuming literally everything under a regularity is a kind of forcing of the issue to make scientific investigation or research simpler and more amenable to explanation.

Finally, Cartwright uses the word ‘interaction’ but not the word ‘regularity’. But if we don’t have regularity, then how can we have a natural law? Or is it really the case that we need regularity even in the cases where we do have instantiations of or subsumptions under a natural law? Perhaps regularity, let alone necessary and universal regularity, simply need not go along with the notion of a scientific natural law. Perhaps we can have lawhood in one and only one case or instance (as in Toovey’s ‘singularist’ account of causation?).

It is because of all this that Cartwright ops for a counterfactual or ‘capacity-ascription’ account of scientific knowledge. That is, natural phenomena have counterfactual capacities or dispositions to do such-and-such in such-and-such situations and conditions, given enough ceteris paribus variables or laws. It’s just that there is no universal necessity or sometimes even regularities involved in these capacity-ascriptions of natural phenomena. All we have is the situation in which we can say that X would, or may, do A, B and C, given situations or conditions D, E, and F, but it is not necessary, or even highly probable, that X will do A, B and C, and it certainly isn’t the case that it is doing A, B and C!

Cartwright gives her own example of a ‘singular causal claim’ thus:

"Acorns have a capacity to give rise to oak trees. Now, I think that’s true and I think that it goes hand-in-hand with a lot of singular causal claims: like ‘That oak tree in my garden came from the acorn we planted there twenty years ago.’ And there are a lot of true singular causal claims like that... without there being any regularity about what would repeatedly happen in any of the circumstances in which an oak tree did result." (202)

What seems to being said here is that all we can have, at least in many cases, are ‘singular causal statements’ but not explanatory regularities. However, this does not seem to rule out the possibility, or actuality, of lawhood or of lawlike or nomological statements (but not generalisations). Is this because of singular causal claim

That oak tree in my garden came from the acorn we planted there twenty years ago.’

contains ceteris paribus laws or specific conditions for the causal process that is being described or explained? That is, it is a reference to a specific acorn and a specific oak tree not to all acorns and all oak trees. Not only that: there is also a reference to a specific garden and a specific act of planting an acorn twenty years ago. Thus unlike most or all scientific generalisations, this is a tensed statement not a time-less one (not an ‘eternal’ sentence, as Quine puts it). In that case, how can it be a scientific statement at all if it is so particular and specific? Perhaps instantiations of lawhood or nomological causation which are also scientific in nature simply do not need to be universal or modal in nature. In other words, not all acorns, by necessity, must grow into oak trees. Perhaps the type of garden or soil must also enter into the equation. Indeed, perhaps things were different twenty years ago in that acorns required conditions that they no longer require or the nature of soil may have substantially changed or changed just a little. However, on a counterfactual or capacity-ascription analysis, given the required set of initial conditions and factors, acorns will grow into oak trees. It’s just that these initial conditions or factors are too numerous or variable to be subsumed ‘under a regularity’ or perhaps even a natural law (or a set thereof).

Cartwright then offers us what she takes to be the ‘standard view’ of these issues:

"You know, the standard view is – take those circumstances and if you had a good microscope and had sufficient time, in every one of those cases in which the singular causal claim is true, you could find some description of the circumstances for that very acorn such that, if only you could repeat those circumstances, there’d be a universal generalisation. Now, I think basically that’s all just a metaphysical pipedream." (202)

What is being said here amounts to a truism. That is, if you had the same circumstances in another case, then the same singular casual claim would be true of that identical set of circumstances and conditions. It follows that if this were repeated for every acorn, then indeed we would have a ‘universal generalisation’. The problem is that these specific circumstances and conditions are not likely to be exactly replicated by another set of circumstances and conditions. This amounts to the claims that if X, Y and Z were the case, then X, Y and Z would be the case. Or, more generously, if X, Y and Z bring about A, B and C, then if X, Y and Z were the case, then A, B and C would also be the case.

There is always the practical problem with finding these universal sets of conditions and circumstances in that one would need ‘sufficient time’ and the requisite equipment to account for this set of conditions and circumstances. One would need an infinite amount of time to account for the sets of conditions and circumstances that would be required to hold down a universal generalisation about all acorns and their growing into oak trees! So not only is this both practically impossible and indefinitely or infinitely complex a task, Cartwright also calls it ‘a metaphysical pipedream’ perhaps born of the metaphysicians desire to bring order out of complexity and simplicity out of multiplicity. In anti-realist terms, even if the metaphysical pipedream were true about acorns and oak trees under a set of conditions and circumstances, what the metaphysician says is the case could not be known to be the case. We would simply not have the requite evidence or data to substantiate or confirm, let alone prove, his ostensible universal generalisation about these or any other phenomena in the natural world. In that case, it is indeed a ‘metaphysical pipedream’ and perhaps says more about the metaphysician’s desire for – or dream of – order and simplicity than it does about the true nature of the natural world.

Despite everything that has been said, Cartwright doesn’t have a problem with what she calls ‘causal happenings’ (203). Indeed why should she? She only rejects modal notions and unjustifiable universal generalisations. This, at least in these respects, is a thoroughly Humean account of causation and natural law. Again, what she stresses instead of these traditional notions of causation and law are singular causal claims:

"So causal happenings are as much part of the fundamental ontology of the world as anything else and then it’s very hard to construct a reason why there can’t be causal patterns – acorns tend to give rise to oak trees and that’s borne out in a lot of singular causal happenings – without there having to be universal generalisations in the background." (203)

So, just like Hume, Cartwright is not against the reality of causation per say; but against the ‘projection’, as Blackburn puts it, of modal properties, such as necessity and universality, onto all acts of causation. Not only that: even without necessity and universality "causal happenings are as much part of the fundamental ontology of the world as anything else" (203). Perhaps it is simply the case that we do not need modal notions or universality in science and perhaps not in philosophy itself. Either that or there simply are no modal properties such as necessity and universality and thus such things are never justifiably projectable or applicable to the natural world. Necessity and universality are just metaphysical notions that metaphysicians stick onto the world and then take to be real ontological properties of the world. In the end they are nothing but ‘projections’ onto the world or psychological ideas, as Hume might have put it.

Finally, Cartwright has no problem with ‘causal patterns’ either, just as long as there are no ‘universal generalisations in the background’ (203). Singular causal events or processes may instantiate causal patterns, as it were; thought they do so without also instantiating a universal generalisation or being subsumed under such a thing. After all, she gives a simple and common example of such a causal pattern. She says ‘acorns tend to give rise to oak trees’ (203). It’s as simple as that really. And that singular causal statement, or statement about a set of singular causal statements, need not assume or bring on board with it anything to do with universal generalisations or any modal notions of any kind. All we require, perhaps even in science, are singular causal statements such as the one just given.

We can conclude with the basic Humean claims that there simply is no such thing as logical necessity, or even metaphysical necessity, in the natural world. Just about everything that Cartwright has said so far follows from that fundamental Humean premise about causation and natural law. Just as we can never infer anything about the future from the conditions of the present. So we can’t even infer anything about another part or aspect of reality now from a given part or aspect of reality – at least not with logical or even a metaphysical certainty born of logical or even metaphysical necessity. Or, as Cartwright puts it:

"Besides, I don’t think that this whole story makes sense, that there’s some description of every circumstance, and if you just went through the whole catalogue of all the properties that obtain on the occasion you’d finally find exactly that arrangement of them that would give rise to repeatability." (203)

Here again we have the formula: If conditions X, Y and Z, then A, B and C will happen. X, Y and Z are the case, therefore A, B and C will be the case (a case of causal modus ponens?). It is of course likely to be the case if one has "some description of every circumstance, and if you just went through the whole catalogue of all properties that obtain on the occasion’ of course ‘you’d finally find exactly that arrangement of them that would give rise to repeatability" (203). The problem if that an account of every circumstance and all the properties which obtain for a singular causal relation or connection will rarely – if ever – be forthcoming. And even if such a thing were possible, perhaps that wouldn’t help much in terms of scientific description and explanation. Of course if the same circumstances and properties reoccur then the same effects will occur. But is this likely? And even if it is, would that in itself get us anywhere?

Cartwright on the Disunity of Science

Strongly connected to Cartwright’s capacity-ascription account, as well as her counterfactual analysis of singular causal claims, is her rejection of the ‘unity of science’ hypothesis as first strongly suggested by Oscar Neuruth. One can see how the disunity of science may follow from Cartwright’s rejection of modal and universal generalisations and the particularity of singular causal claims:

"Now, it’s not that I know that nature is disunified, but I wouldn’t think it was very sensible to build an entire scientific methodology on an assumption that it must be unified. And if it’s not unified, in certain specific ways, then certain specific methodological assumptions that we make in doing science are mistaken, and they’re going to be costly and lead to mistakes, and I don’t want us to make methodological mistakes based on a kind of Holy Grail metaphysics." (204)

It’s not that Cartwright has proved that nature is disunified: it’s just that no one has proved – or could prove – that it is unified. That means that it could indeed be disunified. And if it is, in fact, disunified, then "certain specific methodological assumptions that we make in doing science are mistaken, and they’re going to be costly and lead to mistakes" (204). Perhaps it would be better, then, to simply assume the disunification of nature for methodological or even anti-methodological reasons in that even if we have no conclusive evidence that nature is disunified today, that evidence may well be forthcoming in the future. Indeed wouldn’t it be easier to falsify the unity of science or nature hypothesis than to falsify the disunity of science or nature hypothesis? After all, one concrete example of nature’s disunity, as it were, would falsify the assumption that nature is in fact unified. Whereas no matter how much evidence we may have for nature’s essential unity, it is always possible that some time in the future we will discover something, some phenomenon, which basically falsifies the unity of nature or science hypothesis. This too is a basically Humean point. As Cartwright said about the obsession with universal generalisations and modal property applications that are supposed to be applicable to nature are nothing but a ‘metaphysical pipedream’, so she now says that the belief in the unity of science or the unity of nature is "based on a kind of Holy Grail metaphysics" (204). Just as modal universal generalisations bring order and simplicity and of the multiplicities and the complexity, so the assumption of nature’s essential unity brings order and simplicity out of multiplicity and complexity. In fact the order and simplicity of universal generalisations go along with the order and simplicity that is assumed by the unity of nature or science hypothesis.

Cartwright gives her own reasons why she thinks that scientists, or should I say philosophers of science, feel a strong need for a scientific methodology that is certain, content-less and applicable across the board of all sciences:

"... and now we move on to the new conclusion that there’s no methodology which is certain and has any meat to it, any real ramifications, other than ‘think carefully’ or something like that, which doesn’t really tell you what to do, how do we ensure that we have objective knowledge?" (206)

It is almost as if – or literally is the case – that scientists, or philosophers of science, view scientific methodologies as logicians view the rules of inference or argument-forms or other forms of deductive validity. That is, just as rules of inference secure truth or just correctness for the logician, so methodologies, or even a single methodology, will secure science both truth and objectivity, if not also certainty. But this is not logic and scientific methodologies are never purely – if at all – logical in nature. Quite simply this is because they have content. Logic is primarily about form. That is, science is about evidence or even the truth, logic is about correctness and the forms of logical reasoning or inference. The two worlds, on this account at least, share very little. Even the hypothetico-deductive model is not a case of pure logic being applied to the domain of science. Clearly, the only logical part of the hypothetico-deductive model of science is the ‘deductive’ part. And even that is not purely logical in nature because the contingency of the hypotheses used, and from which we deduce scientific theorems, will pass on, as it were, their contingency or lack of necessity to those theorems regardless of the validity of the deductive inferences that are correctly adhered to.

However, I doubt that any scientist, and certainly very few philosophers of science, would accept a methodology which simply said ‘think carefully’ (206) or ‘don’t generalise too hastily’ or whatever. What they actually want is something with a lot of ‘meat to it’, something which will ‘ensure that we have objective knowledge’ (206). Of course a philosopher like Paul Feyerabend, amongst others, would not even want a scientific methodology which ‘really [told] you what to do’ (206). Why would anyone scientist, or any one else, want that? It would destroy scientific invention and creativity. And creativity and invention, as scientists themselves tell us, is essential to much – if not all – science – and not just theoretical scientific research.

Cartwright herself gives an example of her anti-methodology approach being taken as an attack on scientific objectivity or at least a threat to it. In her case it is her scepticism, if that’s the right word, about the use of probability in science:

"And my attacks, for instance, on being able to use probability as a sure-fire way to infer causes, have come to be seen as an attack on objectivity, tough I’m not at all sure that’s right." (206)

Is the use of probability itself a scientific methodology, or is it something which can be used within a methodology? It is strange then that given the nature of probability theory, that is, that it deals with probabilities not certainties, it is strange that the scientific objectivists, for want of a better term, require that probability gives them ‘a sure-fire way to infer causes’ (206). Probability theory can never give you a sure-fire way to do anything. In addition, I’m sure about this example of ‘backwards causation’, as it were. Do we ‘infer causes’ in science at all? Don’t we primarily infer effects? Perhaps in science we do both. After all, if we chance upon a blackened and smoking forest we can infer the cause – that there has been a fire of some kind. Similarly, if we chance upon a forest fire, we can infer that the forest will soon be blackened and full of smoke. So causal explanation works both from causes to effects and from effects to causes. Is either one or the other of primary importance in science? Perhaps they both are. I’m not even sure how an attack on the fallibility of probability theory is an ‘attack’ on ‘objectivity’ in the first place. Is it simply because probability theory does not give the scientist certainty? In what way is the word ‘objectivity’ being used here? Without an explanation of what precisely the scientific objectivists, or the objectivist philosophers of science, want with their objectivity it is hard to make sense of what they say or what Cartwright is saying here.

Cartwright on Capacity-Ascriptions

Cartwright then goes into greater detail about capacities or what ‘capacity-ascriptions’ are about:

"... I think that you learn about certain situations or certain properties, what capacities they have, and you can also learn about the capacities they have by putting them in very specific circumstances – like, if you put a ball on an inclined plane, and make it as frictionless as possible, and you try to learn from that about the capacity of something with an inertial mass, say, to keep moving unless acted upon by a force to make it stop." (207)

There are two things one can learn about the capacities of ‘certain situations or certain properties’ (207):

  1. The capacities certain situations or certain properties have in themselves. And,
  2. The capacities certain situations or certain properties have ‘by putting them in very specific circumstances’ (207).

One can argue that situations or properties never have certain capacities ‘in themselves’ because neither situations nor properties ever are entirely taken as they are in themselves. That is, both situations and properties are always embedded in particular contexts or sets of conditions and can never be found outside of them. Thus properties and situations act the way they act because they are in specific contexts or conditions. It follows that they never act the same in all contexts and in all sets of conditions. This too will work against our modalising tendencies and our penchant to think in terms of universal generalisations. Thus, in the case of Cartwright’s own example of a ball and an inclined plane which is as frictionless as possible, we will not always be able to come across frictionless planes or even frictionless balls for that matter. Thus is a scientific set-up, as it were. It is an experiment. Thus if we don’t construct these initial conditions we will not learn ‘about the capacity of something, with an inertial mass, say, to keep moving unless acted upon by a force to stop it’ (207). Perhaps frictionless planes do not ever occur naturally, or at least not often. So this experiment, or artifactual set-up, may never actually be replicated in nature – at least not to the full extent required to see what happens to balls when placed upon an inclined frictionless plane. However, this does not mean that we do not learn something about nature even if nature never – or rarely – includes any planes which are frictionless. (Do we find balls in nature? Are they ‘artificial kinds’?)

Cartwright goes into more detail as to why such experiments, or ‘capacity-ascriptions’, are far from being instantiations of a universal generalisation or the containers of modal properties:

"We very often talk about capacities in terms of some characterising behaviour, like, inertial masses have the capacity to keep moving unless something acts to stop them. That’s a characterising behaviour – it’s not all inertial masses do..." (207)

Here we not only have the point that such singular causal claims are by their very nature particular, and therefore non-subsumable under universal generalisation and not subject to modal predication. Though that this very singularity also involves what may be called a selection process in that what is described will ‘not [be] all inertial masses do’ (207). We select this ‘characteristic behaviour’ of balls and inertial masses to explain something particular about a set of natural phenomena. In terms of other explanations or other pragmatic requirements, inertial masses may tell us something that is very different. It all depends on the questions we put to nature. Nature tells us nothing about itself unless we ask it a question. The question here was whether or not ‘inertial masses have the capacity to keep moving unless something acts to stop them’ (207). The answer to this is, yes. That is, if one places a ball on a slightly upturned table, and that table is relatively flat and has no kitchen utensils upon it, then the ball will roll down the slightly upturned table unless something is placed in front of it or if gravity itself is distorted by an outside force, etc.

One of the problems with these experiments, or set-ups, is that one must not only select what it is one wants to find out but one must also select the circumstances and conditions which will tell you what it is you want to know. Different initial conditions will tell you different things and even the same initial conditions can tell you different things depending on what it is one is looking for. As Cartwright puts it:

"Now, that characterising behaviour is often associated with constructing some special circumstances in which that characterising behaviour is exhibited, or almost or approximately exhibited, like the frictionless plane. But the question is, why are those circumstances particularly interesting circumstances? What’s so special about them – they’re after all just some circumstances: you could have this degree of friction, that degree of friction, you might not think about friction at all but something else, you might paint the inclined plane red..." (207)

This simply means that the initial conditions must be selected in the first place. Not only that, but evidently different initial conditions will produce different effects or conditions. Not only that: the very same initial conditions may result in different conclusions for the experimenter depending on the questions he wants answering or the things he wants to test. Thus there is a selection process involved all the way down the line: from the selection of initial conditions to how the same or different initial conditions, or their consequences, are interpreted by the scientific experimenter. This also shows us that there are no such things as pure observations or pure observations sentences, as the logical positivists, such as Carnap, believed. The same set of conditions, and even the same set of observations, will be interpreted in different ways by different observers or experimenters. This will be because they bring along with them different theories and a different set of assumptions through which they interpret the same observations or the same scientific data. Not only do they bring along with them different theories and a different set of assumptions, but the theory they arrive at, or the confirmations they acquire, will result in different theoretical interpretations of what it is they have observed or experimented upon or which they have tested. As they say, ‘theory is always underdetermined by all the data’. That is, the very same data, observational or otherwise, may - or will -result in different theoretical interpretations depending on what the observer wants to know, etc. Even if different observers both want to bring about a ‘frictionless plane', as in Cartwright’s example, the existence of a frictionless plane alone will not guarantee that different observers or experimenters will make the same theoretical interpretations of the same data they have in front of them. In Cartwright’s words, ‘why are those circumstances particularly interesting circumstances?’ (207) Of course what is interesting for one scientific observer or experimenter will not be interesting, or may not be interesting, to another. Again, it depends on their prior interests and what it is they want from the experiment or the observation. For instance, both observers may have some kind of frictionless plane, but what if one wants to ‘paint the inclined plain red?’ (207). This may seem like a silly example but there may be some obscure reason for wanting to paint the plain red. Perhaps the colour-waves of the colour red have some very slight affect on the frictionless plane or perhaps the observer is more interested in the experimental nature of the colour red. The point is that we cannot rule out a priori this outré example.

However, the main point about these variable issues is that they can be divided into two components:

"... we have these two concepts working at once – we have the concept of a capacity and its characterising behaviour, and then we have the concept of interference and distortion and the idea here is that you deploy your concepts of interference and distortion to come up with instances of the characterising behaviour, and the whole point about the characterising behaviour is that it’s behaviour that you learn how to change systematically in order to account for what happens in more complicated circumstances." (207/8)

The point is that these distortions and inferences of ‘characterising behaviour’ will tell us something about such characterising behaviour and the dispositional capacities which underlie them. That if, if such-and-such a thing distorts the initial conditions under scrutiny then we will learn something about these initial conditions and the properties involved in them. Similarly, if we can interfere with these initial conditions, and the capacity-laden properties involved in them, then that interference will tell us something about such properties and initial conditions. What things interfere and distort the properties and initial conditions? Why do they do so? Why are certain aspects of the initial conditions or the properties unchanged by such distortions or acts of interference? What can we learn about the capacities of the properties through such distortions and acts of interference? And so on.

Finally, not only can we introduce distortions and interferences to affect the properties or the initial conditions in order to acquire new information about them, but we will also ‘learn how to change [them] systematically in order to account for what happens in more complicated circumstances’ (207). This shows us that science is not only about observation, testing, confirmation and the creation of theories; it is also about the manipulation of nature or its properties. By such manipulations, such as distortion and acts of interference, we learn much more about nature than we would do simply by observing natural phenomena as they are given to us. The more we play with what’s in front of us, the more we will learn about what’s in front of us. Just staring at a given phenomenon, or set of phenomena, even with the benefit of theory, will not supply us with much when compared to our manipulations of nature that is, after all, what scientific tests and experiments are all about. Thus science has never been just about observing and the mindless cataloguing of all the phenomena of nature. Not only do we demand answers from nature by asking it questions; we often only get those answers by playing with nature – that is, by experimenting on it and testing it. Observation alone cannot come up with all the answers. Not even observation with theory and a set of assumptions can come up with all the answers we want. Only experimentation, testing and other kinds of manipulation of nature will give us all that we want from nature – at least as far as science is concerned.

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