Causal origin and evidence

by

FRANK JACKSON A N D R O B E R T PARGETTER (Monash University and La Trobe University)

MANY have perceived a connection between knowledge about the causal origin of some happening and what that happening may be taken as evidence for. Thus, discovering a relatively mundane causal origin for those experiences dubbed ‘religious’-say , scallops the night before-would undermine their status as evidence for God; and the theory of evolution is widely regarded as a particular- ly powerful objection to the argument from design precisely be- cause of the causal explanation it offers of adaptation. The connec- tion we are talking about is between knowledge of (or perhaps strongly justified opinion about) the causal origin of something and what we may take that something to be evidence for, not that which has been alleged between the fact of causal origin and knowledge. Consider the familiar kind of case where I justifiably and correctly (as it happens) believe it will rain because my barometer has dropped. If this drop is due, unknown to me, to a mechanical malfunction, it is plausible that I do not know that it will rain, although my belief is both true and justified.’ Our concern, though, is with the point that if I know of the malfunction, it seems that I cannot take the drop in reading to be evidence of impending rain.

The connection between knowledge of causal origin and evidence has been widely employed to generally reductionist effect. It has, for instance, been argued that we should not believe in the exist- ence of abstract entities such as numbers, sets and propositions on the ground that, as they cause nothing, nothing can be regarded as a “sign” of their existence, and so nothing can be evidence of their existence.* A less controversial application, because in the realm of

‘See the literature spawned by Edmund L. Gettier, (1963). *See, e.g. , D . M. Armstrong, (1978), vol. 2, p. 46. The argument is most explicit in Armstrong, but is clearly also at work in Hartry Field, (1980), chap, 5. 5 - Theoria 2:1985

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the concrete and contingent, has been against the instantiation of Moorean goodness and of objective but irreducibly non-physical secondary properties. We will focus on this less controversial appli- cation, arguing that considerations of causal origin do indeed pro- vide the germ of a powerful case against Moorean goodness and objective but irreducible redness (say). We will see, however, that the matter is rather more complicated and involved than has been generally realised.

Here is a typical case against Moorean goodness.3 Moore held that goodness was a characteristic of certain states of affairs quite distinct from any of their natural proper tie^.^ How did he know? He granted that goodness as he conceived it was not perceivable by sight, or indeed by any of the senses. Moore held, as he had to, that we know that a state of affairs is good by a special moral sense which yielded an intuition of goodness. But this intuition of good- ness cannot be any kind of causal product of Moorean goodness. We know which properties of happenings around us act causally on us, and they are all natural properties. When an act witnessed by me prompts in me the judgment ‘That’s good’, the properties that do the prompting are all natural ones. No-one thinks that there is some kind of principled gap in the natural sciences’ account of the effect the world has on us which is to be filled by positing the possession of Moorean goodness. But if our intuitions and judg- ments of goodness are not caused by Moorean goodness, if we would have had exactly the same intuitions and made exactly the same judgments whether or not it was instantiated, how can these intuitions and judgments be evidence of the instantiation of Moor- ean goodness?

The usual case against objective, irreducible redness is ~ i m i l a r . ~ How could we know that some object, for instance, a ripe tomato, had it? Presumably, because of the characteristic experience, the

3The fullest presentation we know of the kind of case that follows is by Gilbert Harman, (1977). 4See, e.g., G. E. Moore, (1903). ’It is arguable that what follows is the real argument of John Locke, (1690). Two explicit versions are by J . L. Mackie, (1976), and Frank Jackson, (1977), chap. 5. See also D. M. Armstrong, (1968), and R. J . Hint, (1959), p. 165.

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red-experience, that we typically have when confronted by a ripe tomato. But modern science tells us all experiences caused by external objects, including the red-experience, are caused via action on our brains and central nervous systems. Moreover, this action is fully explainable in terms of these objects’ primary qualities broadly conceived. No-one (almost) thinks that there is some kind of princi- pled gap in the account the physical sciences give of how objects affect our brains which is to be filled by adding objective, irreduci- ble redness to the properties physics, neurophysiology and the like appeal to in their account. But then the red-experience, and indeed all our experiences, are not caused by objective, irreducible red- ness, and so they would have been exactly as they are whether or not such a property is instantiated. Our perceptual experiences, therefore, provide no reason to believe it is ever instantiated-which leaves us with no reason at all for believing in it as a feature of the world around us.

These arguments from causal origin against Moorean goodness and objective, irreducible redness are very appealing. The fact remains that they raise difficult questions.

An initial puzzle is to make good theoretical sense of a passage from matters causal to matters evidential. For the two are prima facie quite separate; the second being explicated, or best explicated as of now, probabilistically, while the first has nothing in particular to do with probability, pace attempts at probabilistic accounts of causality. Moreover, the obvious principles connecting the two that are offered by, or you might extract from, those writers who have brought information about causal origin against Moorean goodness and objective irreducible redness have clear counterexamples. Even if we ducked the theoretical question, there would still be the question of how to respond to the counterexamples.

What principle or principles do the causal origin arguments rest on? There are two, closely related principles which are the most obvious candidates.6

6Some presenters of our causal origin arguments were sufficiently cagey not to state any principles explicitly. But Jackson (1977). was rash enough to nominate (a), and (P) is near enough nominated by Armstrong (1978). ‘ E and ‘ff throughout do double duty as names of events and as names of singular propositions that assert the existence of these events.

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(PI If E is known not to be in any way caused by H, E cannot be taken to be evidence for H.

(Q) If it is known that E would be or would have been the case whether or not H were the case, E cannot be taken as evidence for H.

Typically, when (P) holds, so does (a); and protagonists of the causal origin arguments against Moorean goodness and objective, irreducible redness might well urge that though principle (P) ade- quately serves their purposes, (a) has the advantage of transpar- ency. For why should knowledge that H does not in any way cause E, rule out E being evidence for H? Because such knowledge implies knowing , if confronted with E, that E would have been the case whether or not H were the case; and is it not transparent that then E can be no evidence for H? If you know that the used car salesman would say the car is reliable whether or not it is, you don’t bother to ask.

Supporters of (P) and (a) will, of course, grant these principles are rough and ready. Two queries that come immediately to mind are whether they are as plausible when H i s an hypothesis about the abstract or necessary, rather than about the concrete and contin- gent; and what to say when H is an hypothesis about the future. Presumably we can take present happenings as evidence of future ones without believing in backwards causation or that the present depends counterfactually on the future. Supporters will, though, contend that (P) and (a), taken as applying to the concrete and contingent and as governing how the present can be evidence for the past, and give or take points of detail, are correct.

This is wrong. Without departing from favoured territory we can find clear counterexamples to both (P) and (a).

Newspaper reports on sporting results provide obvious counter- examples to both (P) and (a). The Age and the Sun each send their own reporters to football matches, and they file their reports inde- pendently. This means that when I read in the Age that Carlton won, I know that this report is in no way a causal outcome of the Sun’s report, and that the report in the Age would be just as it is whether or not the Sun had reported that Carlton won, or indeed

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had reported on the game at all. Nevertheless, it is obvious that the Age’s report is good evidence that the Sun reported that Carlton won. (Consistent with all this we may suppose that the Sun comes out rather earlier than the Age.)

Again, consider what we know about stars. It would be absurd to hold that we should only believe in the existence of stars that in some way causally affect us. It is clearly reasonable to believe that we are a tiny, tiny speck in an unimaginably vast universe. That is to say, our experience of those very many and very distant stars that do affect us-gravitationally, via telescopes, and so on-makes it reasonable to believe in the existence, and in some things about the nature, of many even more distant stars that have absolutely no causal effect on us whatsoever. Our experiences would have been exactly the same had these stars never existed, nevertheless our experiences give reason to believe in these stars.

It might be suggested that there is an easy repair to (P), a repair needed anyway to handle evidence about the future. (A similar repair might be proposed to (a), but we concentrate on (P). It will be obvious how to transfer our remarks across from one to the other.) Spots today may be evidence of fever tomorrow, yet the spots are not a causal result of the fever. But of course the spots and the fever have a common cause, say the measles virus in my body. In this case E is evidence for H-despite our knowledge that H did not cause E-arguably because we believe that something that caused H also caused E. Again, although the Age’s report and the Sun’s report do not causally interact, they have a common cause, namely, the game the reporters are watching.

(P*)

Thus we might be lead to

If E is known to be neither caused by H nor caused by something that is a cause of H (possibly a remote one), E cannot be taken as evidence for H.

as the principle on which to rest arguments from causal origin. There are three reasons for not resting the arguments from causal

origin on (P*). First, to do so makes these arguments dubious. Although (P*) is more plausible than (P) and (a), it is nevertheless open to objection.

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Consider a psychologist investigating the effect of alcohol on my reaction time. He would be right to expect similar results for my next door neighbour, who is roughly the same age, weight, exactly the same sex, and so on. These are the kind of results that can legitimately be extrapolated. But we know that there is no causal interaction between my reaction times and his, and, further, there is no obvious candidate to be a common cause of both. We have different parents, the samples of alcohol are different (no regurgita- tion was involved), and so on. Perhaps if you go far enough back in time, you will come across a common cause (Adam and Eve?). But it is hard to believe that you must believe this to be entitled to make the extrapolation. More plausibly, one might hold that you have to believe in a similarity of causes. It is important that I and my neighbour are known to be similar. But these similar causes are distinct, though similar, and so this fact in no way helps (P*).

Or consider the arguments to the existence and nature of stars which are very distant and so causally isolated from us. If the big bang theory is true, it is at least possible that our experiences and these stars have, in the very distant past, common causes. But suppose the continuous creation theory becomes established truth. Would scientists be right to add an appendix to the papers establish- ing it that we should now only believe in the stars that we have, do or will see, or which otherwise causally affect us?

Secondly, resting causal origin arguments on (P*) emasculates them. A believer in objective, irreducible redness can add to his view-or maybe it is already part of it-the claim that the complexes of primary properties which cause our perceptions of red also cause the instantiations of irreducible, objective redness. Similarly, a believer in Moorean goodness can add to his view the claim that the natural properties which cause judgments of goodness also cause instantiations of goodness itself. Neither addition seriously damages their positions, while making them immune from (P*).

Thirdly, there is a better way. We can rest the causal origin arguments against Moorean goodness and objective, irreducible redness on another principle which has the signal advantage that we can demonstrate its soundness using widely accepted theses. We will use the case of Merlin to introduce the required principle.

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Suppose Merlin has no magical powers whatsoever, but that he nevertheless goes around saying ‘Abracadabra’ over seriously ill people. Perhaps he hopes to build up a reputation by virtue of the fact that those who survive live to tell the tale of how he said ‘Abracadabra’, whereas dead men tell no tales. Now suppose that Lancelot is seriously ill, that you don’t know whether Merlin has said ‘Abracadabra’ over him, but do know that Merlin is a charla- tan, and that you are interested in whether Lancelot’s survival would be evidence for Merlin having said ‘Abracadabra’ over him. Because you know that Merlin’s utterance would make no, differ- ence to the progress of the illness, you give equal probability to ‘Had Merlin said ‘Abracadabra’, Lancelot would survive’ and ‘Had Merlin not said ‘Abracadabra’, Lancelot would survive’, for you give each the same probability as ‘Lancelot will survive’. (And, of course, if he does survive and you learn this, all three statements will become certain together, while if you learn that he dies, all three statements will become certainly false together.)

You might express this by saying something like ‘If Lancelot survives, he would have done so whether or not Merlin had said ‘Abracadabra”, and it is tempting to think that this is tantamount to acknowledging that Lancelot’s survival could be no evidence of Merlin’s having said ‘Abracadabra’. But this is too quick. There are mo ways Merlin might be operating. He might be going around saying ‘Abracadabra’ over seriously ill people at random, hoping the fact that dead men tell no tales alone will lead to establishing his reputation. In this first case, it is intuitively evident that should Lancelot survive we would not take this as evidence that Merlin said ‘Abracadabra’ over him.

Alternatively, Merlin might have a special gift for telling when seriously ill people will pull through, and he might say ‘Abracadab- ra’ only when he judges that they will pull through. In this second case, it is intuitive that Lancelot’s survival would be evidence that Merlin had said ‘Abracadabra’ over him. (Think of the cigarette companies’ hypothesis that smoking is a sign, not a cause, of a disposition towards lung cancer. One who accepted this would be right to take the news that Lancelot died of lung cancer as evidence that he smoked, while holding that the smoking played no role in

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his death, and that he would have died whether or not he had smoked.)’

How can we make sense of the fact that Lancelot’s survival would be evidence for Merlin’s having said ‘Abracadabra’ over him, at the same time as acknowledging that ‘Had Merlin said ‘Abracadabra’, Lancelot would have survived’ and ‘Had Merlin not said ’Abraca- dabra’ Lancelot would have survived’ are equiprobable? By noting that in the second case Merlin’s saying ‘Abracadabra’ would be evidence for both subjunctive conditionals. For it is evidence that Lancelot’s condition is not that serious, and so evidence that he will survive. But if he survives, he would have done so whether or not Merlin had said ‘Abracadabra’ over him. Hence, Merlin’s saying ‘Abracadabra’ supports both that ‘Had Merlin said ‘Abracadabra’, Lancelot would survive’ and ‘Had Merlin not said ‘Abracadabra’, Lancelot would survive’. Similarly, Merlin’s not saying ‘Abracadab- ra’ counts against both subjunctive conditionals.

We can now prove that Lancelot’s survival (S) is evidence for Merlin’s having said ‘Abracadabra’ (A). We have Pr (A 0- S) = Pr (A [k S), and, by the argument just given, Pr (A 04 S) < Pr(A O+ SIA), and Pr (A O+ S) >Pr (A El+ S/J. But, provided only that subjunctive conditionals with true antecedents and conse- quents are true, Pr(X O+ Y/x) = Pr(Y/x). Hence we have Pr (S/A) > (S/J. But this can only be true, by the calculus, if Pr(SIA) > Pr(S), which in turn can only be true, using P r W Y ) - WX) , if

P W X ) PdY) Pr(A/S) > Pr(A). Q. E. D.

On the other hand, in the first case Merlin’s saying ‘Abracadabra’ is no evidence for or against either subjunctive conditional, as Merlin says ‘Abracadabra’ at random in this case. Hence we will have interalia Pr(A O+ S) = Pr ( A C b S/A) = Pr(A O+ S) = Pr

’This, of course, is the kind of example much discussed by protagonists of causal decision theories where, roughly, Pr(A E!+ Oi) plays the role classically given to Pr(OUA ); see, e.g., Alan Gibbard and W. L. Harper, (1981). Gibbard and Harper show how the possible worlds analysis of subjunctive conditionals, allied with a “no backtracking” clause, implies that in our kind case, Pr(x smokes [k x gets lung cancer = Pr(x does not smoke b x gets lung cancer).

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(A 0- S/A); then, following the earlier derivation with the appro- priate modifications, we get Pr(AIs) = Pr(A). Hence, as intuition delivered, Lancelot’s surviving in the first case gave no support for Merlin’s having said ‘Abracadabra’.

We are now in a position to solve both puzzles about causal origin arguments. A causal origin argument seeks to show that E cannot be evidence for H by drawing on our knowledge of E‘s causal origins, in particular the fact that they do not include H. Such arguments should be seen as resting on the following principle of causal origin arguments:

(PCOA) If our knowledge of the irrelevance of H to E‘s causal origins shows that Pr(H El+ E) = Pr(H Cl+ E), and if H is no evidence for or against H 0- E, nor H for or against H O-, E, then E is no evidence for H.

We solve the puzzle generated by the clear counterexamples to (P) and (a), and by the dubious nature of (P*), by resting the argu- ments on the distinct principle (PCOA). A principle, moreover, which rests on more than intuition. For, as we have seen in the Merlin case, we can prove Pr(HIE) = Pr(H), from Pr(H O+ E) = Pr(A O+ E ) = Pr(H O+ E / H ) = Pr(H [7-* E/n).

We solve the theoretical puzzle of how to make transparent the way in which knowledge of causal matters implies a result about evidence, by breaking the passage from one to the other into two stages. The first stage is the passing from knowledge of causal matters to the probabilities of subjunctive conditionals. No doubt this stage could be better understood, because the connection be- tween causation and subjunctive conditionals could be better under- stood. But it is not controversial that the two are intimately linked. We have at least made substantial progress. The second stage is the proof given in the Merlin case, which draws simply on the probabil- ity calculus and the widely accepted thesis that subjunctive condi- tionals with true antecedents and true consequents are themselves true.

We can now vindicate the causal origin arguments against Moor- ean goodness and objective, irreducible redness by observing that (PCOA) applies in both cases.

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We know that what causes perceptions of red is some complex of the physical properties of an object’s surface (together with those of its surroundings) though we do not as yet know exactly which complex. Thus, before I look at an object, I know that whether or not it will cause a perception of red in me depends simply on whether or not it has the right complex of physical properties, and that the presence or absence of objective, irreducible redness would make no difference to this. Hence, the probability I give ‘If this object were to have objective, irreducible redness, it would look red’ will be the same as the probability I give ‘If this object were not to have objective, irreducible redness, it would look red’, namely, the probability that I give to the object’s having the right complex of physical properties. (After I look, the probabilities will still be the same, either both virtually one or both virtually nought.) Moreover, learning-no matter how-that this object did or did not have objec- tive, irreducible redness would not be evidence for or against its possession of the right complex of physical properties. Possession of objective, irreducible redness is no evidence about an object’s physical properties nor of their causal powers. Hence (PCOA) applies.

A similar point holds in the case of the argument against Moor- ean goodness. The possession or lack of possession of the kind of property Moore thought goodness was is no evidence one way or the other for the natural properties an act has, nor for their causal powers. Hence, not only are ‘Were this act to have Moorean goodness, it would be judged good’ and ‘Were this act to fail to have Moorean goodness, it would be judged good’ probabilistically on a par, their probability is independent of that of their anteced- ents. Again (PCOA) holds.

Extant versions of causal origin arguments have the defect of focussing simply on H s known causal irrelevance to E, and so on the fact that we give the same probability to (H O+ E) and ( H El+ E). This in itself is not enough to show that E is no evidence for H, witness for instance the Merlin case. What would be provably enough is the additional fact that H is no evidence for or against H El+ E, nor fi for I-? k E. It is plausible that this additional fact obtains in the case of the causal origin arguments against objective,

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irreducible redness and Moorean goodness. Hence we can base arguments against both on (PCOA), yielding successful refutations of both.

Postscript on Epiphenomenalism

The position with Epiphenomenalism is, however, rather trickier.8 Many have argued that Epiphenomenalism leads straight to scepti- cism about other minds on the basis of a causal origin argument. The argument is that epiphenomenalists must allow that another’s screams, say, would be just as loud were he in pain or were he not in pain, precisely because they hold pain to be causally ineffica- cious. How then can his screams be evidence for his pain for the epiphenomenalist? Now it is true that the epiphenomenalist must give the same probability to ‘Were he in pain, he would scream’ and ‘Were he not in pain, he would scream’. But, as we have seen, this is not enough to show the evidential irrelevance of screaming in another to pain in another. It needs also to be the case that the probability of the two subjunctive conditionals is independent of that of their antecedents; and the epiphenomenalist has at least an argument that this does not obtain. The argument is the famous or infamous argument by analogy. The epiphenomenalist thinks that whether or not another screams causally depends on whether or not he has the appropriate brain state; and, though he holds that this state is no causal product of another’s pain, he need not think it evidentially irrelevant. He may argue from his own case, “When I am in pain, I often have a brain state which causes both the pain and screaming. This association in my own case gives me reason to believe that when another screams, he also has a brain state which causes pain as well as the screaming.”

This means that the epiphenomenalist has some sort of reason for holding that the probability of, for instance, ‘Were he in pain, he would scream’ is not independent of its antecedent. For he has a reason for holding that another’s pain is relevant evidence about

‘What follows should be regarded as superceding the unduly (P*) - centred treat- ment in Frank Jackson, (1982).

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whether the state of his brain is of a kind to cause screaming. Hence, we can grant that causal origin arguments are decisive against Moorean goodness and objective, irreducible redness, while being agnostic about whether such an argument forces epipheno- menalists to be sceptics about other minds.

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GIBBARD, ALAN and W. L. HARPER, 1981, “Counterfactuals and two kinds of

HARMAN, GILBERT, 1977, The nature of moraliry, Oxford University Press. HIRST, R. J . , 1959, The problem of perception, Allen and Unwin. JACKSON, FRANK, 1977, Percepfion. Cambridge University Press. JACKSON, FRANK, 1982, “Epiphenomena1 qualia”, Philosophical quarterly, vol. 32,

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Received on December 3, 1984.