Physicalism and Humility

PHYSICALISM AND OUR KNOWLEDGE OF INTRINSIC PROPERTIES Forthcoming in the Australasian Journal of Philosophy Alyssa Ney It is a pretty uncontroversial fact, amongst even philosophers, that science is in a position to tell us at least provisionally what properties there are in the world. Epistemic optimists regarding science endorse the principle that if today’s science is not complete, it is at least on the right track to completeness, positing the right sort of properties that exist. For example, according to Frank Jackson: … it is reasonable to suppose that physical science, despite its known inadequacies, has advanced sufficiently for us to be confident of the kinds of properties and relations that are needed to give a complete account of non-sentient reality. They will be broadly of a kind with those that appear in current physical science… [Jackson 1998: 7] And, if we were ever to have a completed science, i.e. one capable of explaining everything, it would be able to tell us definitively what properties there are in the world. Isn’t it ironic then that starting from such optimism, philosophers have derived arguments for a conclusion recalling Kant: namely, that we can have no knowledge of the intrinsic properties of substances? What could justify this move from ambitious optimism to scepticism? In this paper, I will consider two contemporary arguments for the thesis of Epistemic Humility, that we have no knowledge of the intrinsic properties of substances – one suggested in Rae Langton’s Kantian Humility, and one given by David Lewis [forthcoming].1 Sketched in broad strokes, the arguments start by noting that current science appears to describe the world in purely extrinsic terms. Then, combining the fact 1

A closely related argument has also been offered by Mark Johnston in his provocative [1996]. I will not discuss Johnston’s argument here as it requires separate treatment.

that the properties of science are purely extrinsic with the metaphysical principle that substances must also have intrinsic properties, the arguments reach the conclusion that there are intrinsic properties of whose natures we cannot know. It is the goal of this paper to establish that such arguments are not just ironic but extremely problematic. The optimistic physicalist principles that help get the argument off the ground ultimately undermine any justification the premises give for acceptance of the conclusion. Though I do find these arguments unsound, it is nevertheless worthwhile to consider them in order to see more clearly what should be the methodology of the philosopher inclined to take the discoveries of physical science as having ontological authority. And, I hope, what follows will prompt the physicalist to ask herself – what room is there for metaphysics once physical science is complete?

1. A Contemporary Argument for Humility 1.1 The argument In her work, Langton attempts to make sense of Kant’s claim that we have no knowledge of things as they are in themselves. The thesis of Epistemic Humility is her way of cashing out this claim. Langton provides a very interesting argument for Humility which she attributes to Kant. I will not discuss in this paper the exegetical matter of whether this argument is indeed properly attributable to Kant. Instead, I will focus on a variation of the argument Langton suggests a contemporary philosopher might endorse which shares many details with the Kantian argument [Langton 1998: 179-80]. The worry is that if we take seriously the findings of current physical science as uncovering what the world looks like at a very fundamental level, then we find that it leaves us with

2

significant gaps in the knowledge we can have about the world. The argument may be outlined in the following way: (1) We learn from current science that all fundamental properties are extrinsic. (2) There is no scientific reason to posit intrinsic properties that would serve as the grounds of these properties. (3) But substances do have intrinsic properties, since it is part of their nature that they must. Therefore, (4) Humility: There are intrinsic properties of which we cannot have knowledge. Before discussing what I take to be wrong with this argument, it will help to say a bit about what is meant by ‘intrinsic’ and what is meant by ‘extrinsic’. The common way of understanding the distinction between intrinsic and extrinsic properties is by taking intrinsic properties to be those that an object has due to how it is in itself, and extrinsic properties to be those that an object has due to how it is with respect to other things [Lewis 1983: 111]. One should not confuse the intrinsic/extrinsic distinction with the intrinsic/relational distinction for while the former is one about properties, the latter is one about concepts or about how we describe properties. Moreover, all intrinsic properties can have relational descriptions. Note for example the fact that being rectangular and being the same shape as Central Park actually is are both descriptions of the same paradigmatically intrinsic property, though the first is an intrinsic description and the second is relational [Humberstone 1996; Weatherson 2002]. This said, when considering the Humility argument, we are considering the fact that current science looks to be describing the world’s fundamental properties as all extrinsic.

3

The Short Story: In what follows, I will argue that the problem with the Humility argument is that while the move from (1) to (2) relies on a strongly optimistic version of physicalism, (3) is not a principle a physicalist ought to endorse. It claims the existence of fundamental properties that are not posited by science, but instead by metaphysics. Therefore, such an argument cannot justify the kind of scepticism described by Humility. The justifications for the premises are jointly inconsistent.

1.2 The first premise and strong physicalism At least prima facie, the first premise of this argument is not something that all philosophers would accept. According to Langton, however, this is a premise that Kant would accept. Langton’s Kant had a physical theory according to which the fundamental physical entities were forces, with these forces being dynamic extrinsic properties of substances [Langton 1998: 37-9]. Kant’s physical theory is clearly not today’s orthodoxy. Most contemporary philosophers tend to go along with the optimistic view that current physics is generally on the right track and that the fundamental properties of a completed physics will be something like those properties of today’s microphysics: spin, electric charge, and so on. But who thinks that these properties are extrinsic? Langton cites David Armstrong: If we look at the properties of physical objects that physicists are prepared to allow them such as mass, electric charge, or momentum, these show a distressing

4

tendency to dissolve into relations that one object has to another. [Armstrong 1968: 74-5]2 This sounds somewhat plausible. After all, physicists think of mass in terms of attractive effects on particles. They think of electrical charge in terms of a field produced and effects on the movement of surrounding particles. What is distressing Armstrong appears to be the possibility that all of the fundamental properties of substances turn out to be extrinsic properties – that there are no fundamental intrinsic properties that objects have.3 Now I do not presently want to get into why this should be distressing, what it is precisely that would be wrong about a world with no fundamental intrinsic properties.4 Instead, I would like to focus on what I take to be a tacit assumption of the above passage, which is meant to provide the motivation for the first premise of the contemporary argument for Humility. This premise concerns which properties are the fundamental properties that we have knowledge of, and its claim is that all of these properties are extrinsic properties. What justifies this claim is the observation that the properties physical science talks about all look to be extrinsic.

2

Here we can read Armstrong’s talk of ‘relations’ as talk of extrinsic properties. From what I can tell, Armstrong does not ever talk in terms of ‘extrinsic properties’ but from what he says it should be clear that he is talking about extrinsics, not relational ways of describing intrinsics. For example, an object’s having a particular charge just is a relation that object bears to surrounding particles. One reader was not convinced that Armstrong is talking about extrinsic properties rather than intrinsic properties under relational descriptions in the above passage. Fair enough. However in this section I am interested in developing an argument starting from the observation that the properties of physical science all look to be extrinsic. In a later section, we’ll look at a distinct argument that considers the possibility that the properties of physical science are known only under relational descriptions. 3 A quick comment on this first premise. As stated it says that current science tells us that all fundamental properties are extrinsic. I should mention that I do not have in mind here the claim that scientists in their practice make any claims like ‘This is a fundamental property’. Rather, the idea is that the sciences tells us which properties exist and we as philosophers may take such claims to be equivalent to claims regarding which properties exist fundamentally. 4 I highly recommend John Hawthorne’s [2001] for a persuasive overview of what is bad and what is not so bad about this view according to one model, causal structuralism.

5

But I think we should ask, why think that only physical science has the legitimacy to dictate which properties are fundamental? What is underlying the first premise is precisely the assumption of strong physicalism. Physicalism is ordinarily construed quite simply as the view that everything is physical or sometimes as the view that everything supervenes on the physical.5 I will use ‘strong physicalism’ to refer to the stronger and more precise doctrine according to which the fundamental properties, i.e. the properties that all other properties depend on, are just the properties of physical science.6 In other words, the strong physicalist believes that only the physical sciences have the ontological authority to ‘tell us in their own terms what the world contains’ [Crane and Mellor 1990: 186]. Following Philip Pettit, strong physicalism is the ‘doctrine which holds, roughly, that the empirical world “contains just what a true complete physics would say it contains”’ [1993: 213]. For the purposes of this paper, it will not be necessary to get clear on what precisely lies within the boundaries of physical science, but to be sure this includes physics. Strong physicalism rules out any properties other than those of physical science being fundamental. This version of physicalism is stronger than a more ordinary version, supervenience physicalism, in that it goes further than merely saying that everything is physical and that everything supervenes on the physical in supposing that there is a strong asymmetrical dependence between the properties of physical science and all other properties.7 The optimistic version of strong physicalism that lets us move from the first 5

This is for example Daniel Stoljar’s way of defining the view [2001]. I’m going to sidestep issues resulting from Hempel’s Dilemma here which some take to show that there is no way to define physicalism in such a way that it is neither obviously false nor trivial. A discussion of this problem would take us too far afield, however in what follows I will take physicalism to be a thesis asserting the ontological authority of a future, true, complete physics. 7 One easy way of seeing that mere supervenience does not entail asymmetric dependence is to consider a case of Leibnizian preestablished harmony. Imagine a situation where cases of As co-occurred with cases 6

6

to the second premise adds the claim that current physical science is on the right track to discovering the fundamental properties of reality. So, if current physics is formulated solely in terms of extrinsic properties, the fundamental properties of reality are wholly extrinsic.

1.3 The second premise The second premise of this argument states that there is no scientific reason to posit intrinsic properties that would serve as the grounds of the extrinsic properties physical science talks about. This follows from the first premise combined with the facts that (i) current physical science is on the right track and (ii) current physical science has the ontological authority to say what all of the fundamental properties are. However, it is worth emphasizing the consequences that the first premise has for the strong physicalist that endorses it. So that we may get clearer on these consequences, let us take the example of one of the purported extrinsic properties of physics: unit positive charge. Imagine that physical science is completed and a list of all of the fundamental properties (those that appear in this completed theory) is made. Let’s say that unit positive charge is on the list, and that it along with all of the other properties on the list are extrinsic properties. But now, one might think that there must not be just extrinsic properties, but also intrinsic properties that serve as their grounds. So let us ask ourselves: what could serve as the intrinsic ground of unit positive charge? Well, it seems, whatever intrinsic of Bs simply because God set it up to happen that way at the beginning of time. Here there would be supervenience of As on Bs and vice versa since you could not have the changes in the one without changes in the other. We could even imagine that since God willed it, the correlation between As and Bs was a matter of law. Still, we would not have any asymmetric dependence of either the As on the Bs or vice versa. The As are not there because of the Bs, nor are the Bs there because of the As. In this scenario, rather, both are dependent on God. This point, that supervenience, even strong supervenience, does not entail asymmetric dependence is also elaborated by Jaegwon Kim [1993: 67].

7

property it is that is responsible for repelling other things with unit positive charge and attracting those with negative charge – the intrinsic correlate of positive charge. We cannot say anything more about the ground than this. After all, by hypothesis physics is complete and it didn’t mention the existence of this intrinsic property that is the causal ground of positive charge. In addition, we certainly do not get evidence about this property from everyday experience. So, to introduce such a ground would be akin to introducing a dormitive virtue – positing a nondescript something just to ground the relation. Langton offers a similar pattern of reasoning involving an example from the modern period. She asks if scientists posited impenetrability (taken to be the extrinsic property of not being able to be penetrated by other objects) as part of their theory, what reason would there be to posit a distinct intrinsic property – solidity – just to serve as its ground? Langton says, ‘How does the positing of solidity help to explain anything? What more could there be to know?’ [1998: 176]. Following this reasoning, the strong physicalist ought to say that these grounds simply do not exist, for they would be explanatorily otiose.8

8

It would be wrong here to let his argument rest without responding to the very influential argument of Elizabeth Prior, Robert Pargetter, and Frank Jackson [1982] that dispositions necessarily have separate categorical (i.e. nonextrinsic) causal grounds; therefore, a short digression is in order. In the present paper, the concern is not with the grounds of dispositions per se but more generally with intrinsic grounds for extrinsic properties; still their argument is worth considering. The main support they provide for their view is the claim that for each action, there must be a causally sufficient basis for that action. Even if we allow Prior et. al. are right that there must be a causal basis for each action, e.g. the breaking of a glass, keeping in mind the option of adopting causal structuralism, it does not follow that the causal basis is not identical to the disposition (or extrinsic property) itself. The flaw in Prior et. al’s argument is that they have ignored the option of causal structuralism, the view according to which there are no intrinsic properties [Shoemaker 1998; Hawthorne 2001], and so all of their arguments rest on the mistaken dichotomy that either dispositions are identical to intrinsic grounds or have separate intrinsic grounds. Prior et. al. do have an argument that dispositions are not identical to their causal bases, but this argument is based on the assumption of multiple realization, that there are multiple possible intrinsic bases for each disposition. If causal structuralism were true though, there would not be multiple intrinsic realizations for the simple reason that there would not be intrinsic anythings. Therefore, there is some reason to think that it does not follow necessarily from the nature of a disposition (or in our case, an extrinsic property) that it have an intrinsic causal ground. I am not here providing an argument for the truth of causal structuralism.

8

If physical science is saying that these extrinsic properties like unit positive charge are the fundamental properties, then it is wrong to posit something more fundamental to serve as their grounds. Ideally, we talk about grounds because we think that by doing so we will be able to better understand what is grounded. However, if we assume strong physicalism, positing something more once physical science has already explained everything will not help us better understand anything.9 Moreover, supposing that there are intrinsic grounds for the extrinsic properties of physical science amounts to supposing that the extrinsic properties of physical science are not truly fundamental, in that they depend on something else, something intrinsic.

1.4. The third premise: intrinsic properties The third premise is that substances have intrinsic properties. We have already seen from the second premise that whichever intrinsic properties substances have, these will not be those that ground the extrinsic properties that are fundamental, for as we have seen, nothing is needed to ground these. So the defender of this argument does not believe that substances have intrinsic properties in order to ground extrinsics [Langton 1998: 120, 180; 2004: 133]. Instead, it is for a different metaphysical reason that substances are said to have intrinsic properties. This reason falls out of pretty uncontroversial and widespread conceptions of what it is to be a substance and what it is to be an intrinsic property. Let us start with the latter. Recent work regarding the nature of intrinsic properties shows that we do not yet have a received view regarding the necessary and However, the possibility of causal structuralism entails that Prior et. al. have not shown that necessarily, dispositions (or extrinsic properties) must have intrinsic grounds. 9 This is what I take to be the main thrust of Langton’s discussion at [1998: 183-4].

9

sufficient conditions for something to be intrinsic. Nevertheless, I think we can say two things. First, we can say that an intrinsic property is one that is shared between duplicates [Lewis 1986: 61-2]. So, for example if being a sphere is intrinsic, and this tennis ball is a sphere, then all duplicates of it must also be spheres. This is a necessary but not sufficient condition for a property to be intrinsic. To see why, note that for any x, the property of being a duplicate of x is shared by all duplicates of x though being a duplicate of x is plausibly extrinsic [Dunn 1990]. A second necessary condition for a property to be intrinsic is that it be the kind of property that something can have when it is lonely.10 Say something is lonely if and only if the only other objects it exists with (ignoring those necessarily existing things such as God perhaps or numbers) are its own parts. As Lewis once demonstrated, this is also not a sufficient condition for something to be intrinsic, since the indisputably extrinsic property loneliness also satisfies this condition [Lewis 1983: 197-200]. We can ensure that loneliness does not count as an intrinsic property by requiring that for something to be an intrinsic property it must at least be such that an object can have it when it is lonely and also when it is accompanied. Perhaps this is a necessary and sufficient condition. Now, why must substances have intrinsic properties? One argument suggested by Langton [1998: 49] asks us to step back and consider what it means to be a substance. According to a popular conception going back at least to Aristotle, it is necessary that for something to be a substance, it must not be dependent on any other thing. A substance should not be dependent on any other thing wholly distinct from itself, for example, on 10

To be more precise, following Langton and Lewis [1998], we can say that an intrinsic property is the kind of property whose instantiation is compatible with loneliness and lawlessness. So, an intrinsic property is the kind of property an object could have at a world with no other wholly distinct objects and where there are no laws of nature. This necessary condition on intrinsicness makes it such that powers or dispositions objects might have do not count as intrinsic properties.

10

anything that is not a part of itself. To understand what this means, we might consider a plausible principle governing possibility – the Humean recombination principle. This principle says that anything can exist or fail to coexist with anything else [Lewis 1986: 87-8]. Employing this principle, we can say that it is part of what it is to be a substance to be such that it possibly exists lonely at a world. But it is not possible for a substance to exist without properties. And what kind of properties could a substance have when it is the only thing in the world? Well, the type of properties that an object can have when it is lonely: intrinsic properties. Thus, substances must have intrinsic properties, at least when they are lonely. Once we have established that lonely substances must have intrinsic properties, it is a simple task to establish the more general conclusion that all substances (lonely or not) must have intrinsic properties. To see this, consider a substance s that exists at this world. It seems possible again applying the Humean recombination principle that there may be an intrinsic duplicate of s alone at a world. That is, it seems true that there could have been a world with just s as it is now intrinsically. Now if there could be a duplicate of any substance as it is now lonely at a world, then this substance as it exists now must bear intrinsic properties. If it did not presently have the sort of properties that an object could have were it lonely, it could not possibly exist at a world as it is now except lonely. Unfortunately, this argument for the conclusion that substances must have intrinsic properties is unsatisfactory for at least two reasons. First, the argument depends on the Humean recombination principle. Although Langton, Lewis, and others who endorse Humility arguments may accept such a principle, many others do not, and some might even find the appeal to such a principle question-begging. More importantly

11

however, the argument is not sound since as we have already seen, lonely substances do have extrinsic properties – loneliness is precisely such an example. Thus, it would be best to search for another argument. It was suggested to me (by Ted Sider) that the conclusion that all substances have intrinsic properties can be had much more cheaply via the following argument. Consider any case of a possibly instantiated intrinsic property, P. It seems that both having P and lacking P must be intrinsic properties. If having P is a feature of an object based solely on how it is with respect to itself and not other things, then lacking P (having not-P) must also be a feature an object has solely due to how it is in itself. So, it must be the case for any substance that it either it has P or it has not-P. Therefore, if it is even possible for there to be an intrinsic property that is instantiated, all substances have intrinsic properties. Some of my readers may prefer this simpler argument.11 A third argument for the third premise is based on the conviction that we need intrinsic properties to “fill in” the world and explain what makes objects resemble each other, what makes them similar or dissimilar. I believe this is the sentiment Quine has his McX give voice to in “On What There Is”: ‘… these houses, roses, and sunsets, then, have something in common: and this which they have in common is all I mean by the attribute of redness.’ For there being attributes is even more obvious and trivial than the obvious and trivial facts of there being red houses, roses, and sunsets. [Quine 1953: 10].

11

Of course one is free to object that it is not even possible for there to be an intrinsic property that is instantiated, however I cannot see what an argument for this claim would look like. There doesn’t seem to be anything incoherent about the idea of an intrinsic property. Rather, it is just that the physics of our world is not such as to warrant us in believing in any.

12

Quine is far from agreeing with McX here, but of course the idea is the familiar one that there must be something in virtue of which objects resemble each other. Since intrinsic properties are those shared between duplicates, it would seem that it is precisely intrinsics that are needed to fill in the world in this way.12 These are some defenses that might be offered for the third premise in the argument for Humility. Langton suggests that Kant’s argument is along the lines of the first defense, however barring the problems with that argument, the idea that substances must have intrinsic properties is taken to be fairly uncontroversial in the metaphysics literature, even if it rests on no more than the intuitive pull of McX’s thought.

1.5. Getting to Humility The argument closes itself in the following way. From the first premise we learn that according to physical science, the fundamental properties are extrinsic properties. Assuming that current physical science is on the right track to providing a complete list of the fundamental properties, we can conclude that these properties do not have intrinsic grounds. But, according to the third premise, substances do have intrinsic properties. So it follows, substances have intrinsic properties that we cannot know about.

2. What’s Wrong with the Argument Now that the assumptions behind the Humility argument are out in the open, it is likely evident where the inconsistencies lie. The problem I find with the argument is that the motives behind (1) leading to (2) combined with these premises’ truth would lead one to

12

I take this sort of reasoning to be motivating Armstrong [1997], and Lewis [1999] to believe that objects must have intrinsic properties.

13

reject (3). If you believe that physical science is in a position to state which properties are fundamental, and it says that only extrinsic properties are fundamental, then assuming these extrinsics don’t need intrinsic grounds, why believe that there are other nonextrinsic, i.e. intrinsic properties that also exist and that we cannot know about? The third premise, no matter how well justified it is by the received metaphysical conception of substance is inconsistent with the first two premises plus the assumptions of strong optimistic physicalism. The strong physicalist doctrine takes it that completed physical science describes wholly what properties there are at the most basic level and there is no room for metaphysical doctrine to say anything more, adding more properties to this list. But isn’t there a weaker variant of (1) that can be exploited in order to divert my criticism of the argument? Could one choose not to adopt strong physicalism and then still be led to the conclusion of the Humility argument? One might shift from premise (1) to instead adopt the following (1*): (1*) We learn from current science that all of the fundamental scientific properties are extrinsic. This weaker claim leaves open the possibility that there may be other fundamental properties that we may learn about in some extra-scientific way. (1*) is consistent with, yet does not assume, strong physicalism, and when it is inserted into the argument, it produces an argument for Humility immune to my objections. Fair enough, however those to whom Langton addresses her argument would accept not just (1*) but also the stronger (1). Dualists, idealists, Kantians: those are the types that could take this way of defending the Humility argument, but not today’s physicalist orthodoxy.

14

Another issue that needs to be addressed here is whether we do in fact learn about certain intrinsic properties through ordinary experience so that the Humility thesis turns out to be trivially false. For example, consider the property having five parts, or being spherical. These properties both bear the marks of intrinsicness. They are the types of properties that would be shared between duplicates. They can be instantiated by a lonely substance. And yet we may have knowledge of these intrinsic properties quite easily via ordinary perceptual experience – no metaphysical speculation required. I take it to be an interesting question whether or not properties which are dependent on fundamental extrinsic properties may be intrinsic. That is, if we assume that all fundamental properties are extrinsic, then I am not sure whether it could be the case that there are non-fundamental properties that we learn about in experience which are ontologically dependent on those extrinsics and yet intrinsic. I don’t have an answer to this question. But to demonstrate how a positive verdict here would not make the Humility thesis falsified almost trivially by ordinary experience of intrinsic properties, we must draw a distinction between two kinds of intrinsic properties. Say that a property is derivatively intrinsic iff it is intrinsic and yet its instantiation is ontologically contingent on the instantiation of other properties. Call a property a nature-revealing intrinsic iff it is non-derivatively intrinsic. A revised Humility thesis claims that we cannot have knowledge of nature-revealing intrinsics. This is consistent with the conjecture that we may have knowledge of derivative intrinsics though we have no knowledge of “the nature of things” in a salient respect.

15

I will return below to the issue of where we go from here; that is, what we may learn from the Humility argument by having to deny one or more of its premises. For now, let us consider a slightly different Humility argument offered by David Lewis.

3. Lewis’s Variation on the Argument As noted above, Lewis has proposed a variation on the Kantian Humility argument. I will say a bit about this second argument because I think many philosophers will find this one more plausible than the first. The first argument presupposes the existence of groundless or “brute” extrinsics. Some philosophers may have been put off by this, thinking in response to the argument in Section 1.3 that even if the grounds of the extrinsic properties turn out to be akin to dormitive virtues, they should still be accepted because the notion of a brute extrinsic property is incoherent or otherwise unappealing. Lewis’s argument, on the other hand, does not make use of brute extrinsics. The principal idea behind Lewis’s version of the Humility argument is that the sciences postulate properties by describing causal roles. All of the knowledge we can have about the world is in terms of these causal roles. But we can have no identityrevealing knowledge of the fundamental intrinsic properties that occupy these roles. Lewis argues that (1) to the extent that we know of the fundamental intrinsic properties of things only as role occupants, we have not yet identified these properties, and (2) no amount of knowledge about which roles are occupied will tell us which properties occupy which roles. The simplest way to see this point is to consider a case where we have scientific knowledge of a causal role. For example, we learn about property X by seeing that there

16

is a property such that when an object has this property, we get visual response R when we look at it and the object tends to affect other objects in a particular regular way. By learning about the role that X occupies, we may learn a lot about how it acts at this world. Still, Lewis argues, we have not learned anything about the identity of X. Why is this? Well, because it seems as if we can imagine a world where property X and a distinct property Y switch causal roles. So at this world, call it ‘w’, property X occupies the causal role property Y occupied at the actual world, and property Y occupies the causal role property X occupied at the actual world.13 It seems clear that if we agree with Lewis that w is a possible world, then we cannot discriminate between the situation described by w and the situation we find in the actual world. Any evidence we have for believing property X is instantiated on a given occasion is causal evidence. It is evidence that a type of causal role is being exemplified. However since it is possible for all we can tell that it is property Y rather than property X that is occupying this particular causal role, we can never know that we are being presented with an instantiation of property X rather than property Y. Lewis argues in his “Ramseyan Humility” that this argument extends to apply to most or all fundamental properties – that we can know nothing about their identity – that we can only know the causal roles they occupy. As we can see, Lewis’s argument is like the Kantian one of Langton in that it makes a case for the claim that we can know nothing about how substances are in themselves. This argument is different however in that it does not rely on there being any ungrounded extrinsic properties. The extrinsic properties Lewis’s argument deals with would be those which constitute causal roles. And it is clear from Lewis’s argumentation 13

Of course, none of this reasoning depends on Lewis’s controversial modal realism as defended in his [1986]. One could, for example, think of the example in terms of a conception of possible worlds as abstract representations of ways things could have been.

17

that he sees these roles as occupied by intrinsic properties. It is in this way, by constituting causal roles occupied by intrinsic properties that we can see extrinsic properties as grounded on this picture. But precisely because extrinsic properties are not in general ungrounded here, Lewis’s argument is not pointing to any real sceptical problem. For Lewis, we gain evidence of intrinsic properties by learning about how substances are related causally. So, if physics is indeed positing an intrinsic property such that it occupies such and such causal role, then we have thereby learned about an intrinsic property; we have learned how an object is in itself.14 The putative fact that we could not distinguish whether it was really X rather than Y that is occupying the role on a given occasion does not undermine the fact that we can learn a lot about the intrinsic properties postulated by science via causal roles. This is just to make explicit the fallibilism that most philosophers accept in formulating their anti-sceptical epistemologies. One can have knowledge of a proposition without being able to rule out all sceptical alternatives to that proposition. For example, on a simple reliabilism or evidentialism, I can have knowledge of intrinsics so long as I either form beliefs about them using a reliable belief forming mechanism, or have evidence of their existence from experience. If intrinsic properties exist and are actually instantiated, then satisfying these conditions certainly will not require an additional capacity to distinguish the actual world from one in which the experiences or beliefs are caused by a different intrinsic property playing the same causal role. As Langton herself has pointed out, indeed, even according to Lewis’s own contextualist theory, one can truly say in most contexts that ‘one knows a particular intrinsic property is instantiated’, even though one may not be able to rule out 14

Jonathan Schaffer [forthcoming] provides an extended development of the claim that virtually any contemporary epistemological view entails that by knowing causal roles, we may have knowledge of the intrinsic properties that occupy them.

18

the possibility that this property has not been swapped with another which is implementing its causal role [Langton 2004: 134-5]. At least such statements will be true in a context so long as one is not explicitly considering the swapping argument, thus making the sceptical alternative salient. So, given certain plausible fallibilist theories of knowledge, Lewis’s swapping argument does not demonstrate that we cannot have knowledge of intrinsic properties (or at least that in most contexts we can be truly said to have knowledge of the intrinsic properties of substances). The real issue with Lewis’s Humility argument, however, that makes it much less compelling than the Kantian one is that it seems to be trading on the intrinsic/relational distinction rather than the intrinsic/extrinsic distinction. For the proponent of the argument in Section 1, by doing science we only learn about fundamental properties as extrinsic properties. However, for Lewis, by doing science we only learn about the fundamental properties of things as occupants of roles. But this, of course, does not mean we are only learning about extrinsic properties. Consider the example from the beginning of the paper which I used to demonstrate the difference between relationality and extrinsicness. I can learn about the property being rectangular by learning that it is the property of being the same shape Central Park actually is, but of course ‘being the same shape as Central Park actually is’ is just another way of describing being rectangular; and indeed it is part of being rectangular’s role to be instantiated by Central Park. To sum up, though Lewis’s argument may be preferable to the Kantian one since it does not rely on there being ungrounded extrinsic properties, it is ultimately unsatisfactory since it does not generate a genuine sceptical scenario. If anything, Lewis’s argument shows us that we can only learn about intrinsic properties under their mode of presentation as

19

relational concepts; it does not show us that we cannot learn and hence have knowledge about intrinsic properties under any mode of presentation. Therefore, we can agree with Lewis and yet still believe we can learn how things are in themselves.15 This is not the case for the Kantian argument. On its terms, we cannot learn about intrinsic properties by learning about the extrinsic features of the world. Since the role of the intrinsics is not to ground any extrinsic properties, we could not pick out a given intrinsic property using a phrase such as ‘the intrinsic property that is a ground for this extrinsic property’ or ‘a ground for this causal role’. Assuming we know substances must have intrinsic properties for the metaphysical reasons listed in Section 1.4, this will tell us that there are intrinsics, but it won’t give us any way to gain knowledge of any particular one, in the way that we could if they were the realizers of causal roles we had access to.

4. Tension between Physics and Metaphysics 4.1 The Limits of A Priori Extrapolation Getting back to the argument of Langton that we started with, one might object to this discussion that in arguing against Humility, I have conflated the principles of strong physicalism with the principles of logical positivism, assuming that there is no room once physical science has given its list of properties for us to posit more intrinsic properties. I certainly do not want to rely on positivistic assumptions regarding the impotence of metaphysics in order to guard against Humility. Therefore, I must take this objection seriously. Is it indeed the case that strong physicalism can allow that the list of

15

Thanks to an anonymous referee for help in clarifying this point, as well as the discussion in the previous paragraph.

20

fundamental properties posited by physical science could be supplemented should metaphysical considerations deem extra properties necessary? One might ask, what about a version of strong physicalism that says: (SP’) All properties depend on those which physical science says exist and which can be extrapolated a priori from what physical science says. This seems to be the kind of physicalist Langton is addressing; one who believes physical science has its say regarding the list of properties, and then that it is up to us as philosophers to, using a priori methods, extrapolate further properties entailed by the physical picture.16 Whether or not employing such a methodology will lead one to adopt an ontology consistent with strong physicalism, however, depends on how the extrapolation goes. It would appear that the extrapolation could work in one of two ways: A. There are certain properties mentioned by physical science whose existence entails the existence of other properties, which are then extrapolated a priori. B. Once we see the complete or near-complete list of properties physical science mentions, using a priori reasoning, we may conclude there must be more properties of a certain kind. It is not that the existence of the physical properties themselves (de re) entails the existence of any other particular properties, but instead that the list as a whole appears incomplete due to a priori reasoning. The procedure described by (A) is compatible with strong physicalism as it is ordinary understood. For, since the extrapolated properties are entailed by the properties of physics, they bear a dependence relation to them, and so are physicalistically

16

Thanks to an anonymous referee for pressing me here.

21

acceptable.17 This is precisely what allows the physicalist functionalist to posit the existence of properties he finds to be functionalizable, for example, intentional properties. If a particular intentional property is to be understood as the higher order property that there is some other property P which implements a particular functional role, then the existence of such a P which plays that role entails the existence of that intentional property. If P is a physical property, then if it in such a way entails the existence of the intentional property, then the intentional property is thereby physicalistically acceptable.18 On the other hand, the extrapolation described by (B) seems quite different, and yet seems to be precisely what the Kantian argument is suggesting occurs when we posit intrinsic properties on the basis of a physicalist worldview constituted wholly by extrinsics. It is not that the existence of any of the particular properties mentioned by physical science entails the existence of intrinsic properties. The arguments cited earlier (Section 1.3) certainly did not make use of any assumptions regarding the nature of the individual properties on physical science’s list. Rather the idea is, once we get a feel for what physical science’s final list of properties will look like, we as philosophers, motivated by metaphysical considerations from the armchair conclude this list must be incomplete. For the denial of fundamental intrinsic properties appears incoherent. However, this is not enough to make these additional properties physicalistically acceptable. Their existence is not entailed by the existence of the properties on the physical scientist’s list, and so they do not therefore depend on the existence of the fundamental physical properties. There is no entailment even from the entire list of 17

Well, it’s not quite that simple. For the entailed properties to be physicalistically acceptable, they must not bring with them new causal powers. But let’s ignore this complication for now. 18 This is the way the extrapolation of intrinsics works for Lewis.

22

extrinsic properties to the existence of intrinsic properties. After all, it isn’t the existence of those properties on science’s list which is supposed to entail the existence of intrinsics but instead the further assumption that that list is exhaustive.

4.2 Causal Closure Thinking that we would need a metaphysical postulation of properties to facilitate explanations of physical phenomena would also appear to threaten the causal closure of the physical domain, a principle that most philosophers take to be essential to physicalism. The guiding idea of the causal closure principle is that in order to explain any physical event, one need only appeal to physical causes. One need not go outside of the domain of physical science to give an explanation of a physical event.19 The metaphysical postulation of intrinsic properties suggested by the above methodology appears to challenge the causal closure of the physical by suggesting that we do sometimes need to go outside of physical science to explain physical phenomena: we need to do so in order to posit intrinsic bases for the fundamental properties, should all of the properties posited by a completed physics turn out extrinsic. I am arguing here that this methodology is confused. We do sometimes go outside of physics to posit properties that are not straightforwardly seen as physical causes; for example, when we posit mathematical entities. Nevertheless, these postulations are backed up by substantial physical theory and many would argue that we need these mathematical entities to facilitate physical explanations. This is not so however regarding the postulation of intrinsic properties to ground extrinsic properties. Doing so seems to have no clear way

19

To be more precise, the causal closure principle as I am understanding it says: if a physical event has a causal explanation at a time t, it has a physical causal explanation at t.

23

of enhancing physical explanation. Moreover, when we posit mathematical entities, we are not providing additional causal explanations for phenomena. Therefore, the existence of mathematical explanations would not seem to threaten causal closure. Yet presumably, one would take these intrinsic properties to be causally relevant. If this is the case, then one might think doing so would threaten the causal closure of the physical domain. It is a further interesting, albeit a bit peripheral, question whether this sort of critique also extends to Lewis’s picture. To see this, let’s set aside the objections I raised to Lewis’s argument in Section 3. Recall Lewis’s view that the properties we discover by means of science and ordinary experience are higher order properties which are instantiated when there is some intrinsic property or other that plays the higher order property’s constitutive causal role. Some have thought, following the exclusion arguments of Kim [1998, for example] that a functionalism of this sort about a subset of these properties Lewis is interested in, mental properties, entails an epiphenomenalism about mental properties. The worry is that due to causal closure, the realizers of functionalisable mental properties exclude the mental properties from having any causal relevance. One might ask whether this exclusion problem generalises to threaten the relevance of all properties we may learn about on Lewis’s view. So that we may examine this issue, consider any putative case in which one of his functionalisable properties, call it ‘F’, is causally relevant. According to Lewis, at the time that F is instantiated, there will also be another property, the intrinsic realizer of F, instantiated. Now we may ask: what is really responsible for the effect? Is it the instantiation of F or the instantiation of F’s realizer; call it ‘R’? Since according to Lewis, an instantiation of F is distinct from

24

the instantiation of one of its realizers, it looks like we have two distinct causes of the effect, the exemplification of F and the exemplification of R. Since this case generalises to all functionalisable properties, it looks like every case of causation involving the properties we learn about through science and experience is overdetermined according to Lewis. For those sympathetic to the intuition that causal overdetermination is not this widespread, this is an untenable result and so one or the other of F or R’s causal relevance has to go. So one has to choose: either it is the functionalisable physical properties that are causally efficacious or their underlying intrinsic bases.20 Given the fact that the intrinsic properties are the ones that are supposed to implement the higher order properties’ causal roles, there is reason to say that it is only the intrinsic occupants that have causal powers. But these are not the properties we learn about through physical science. So it looks as if the properties of physical science have been drained of their causal efficacy. This is indeed a strange version of physicalism to uphold, one which denies that all physical events have physical causes, and hence causal closure of the physical domain. Alternatively, one may uphold causal closure and instead say it is the intrinsic grounds that are drained of their causal relevance. But then it is fair to ask, why posit the existence of properties that do no causal work? If one accepts my earlier arguments that Lewis is not really pointing to any sceptical problem, then we can avoid this result. We can claim that we do learn about intrinsic properties via physical science and that these causally relevant properties exclude their higher order, functional

20

I should say, for full disclosure, that I do not as a matter of fact think such exclusion arguments are sound, primarily because I do not believe there is anything wrong with accepting widespread and even systematic causal overdetermination. I have argued this elsewhere. Still, as a majority of philosophers do tend to take such arguments seriously, it is worth pointing out that if one wants to adopt Lewis’s picture, one will have to find a way to respond to this type of argument.

25

counterparts from having causal relevance. Otherwise, we seem left with the above dilemma.

5. Three Options If like me one is dissatisfied with the arguments for Humility, but one still accepts the fact that the properties of current physics all look to be extrinsic, then one is left with three options. Option #1: One can accept strong physicalism but deny epistemic optimism. This option involves accepting that only physical science can say what the fundamental properties are, but denying that current science has even an approximately correct conception of the fundamental properties since there must be at least some intrinsic properties on the final list. Perhaps such a person would say: physics is not complete unless it has described for us the intrinsic grounds of the extrinsic properties of current science. One might get around the objections of the previous section by insisting that it is not metaphysics that should be responsible for positing the intrinsic grounds, but science itself. Perhaps there is a fundamental level of reality not yet discovered that involves atomic particles with properties of a categorically different kind than those of today’s theories. There is no doubt that one could hold out for such a possibility, however it is not at all clear to me that this would be rational. After all, today’s physics is very good at explaining the behaviours of ordinary objects. It is unclear therefore why we should not believe it is on the right track. In order to believe the physical theories are fundamentally off, it seems there should be some range of physical phenomena that it is not able to explain. Surely there are some phenomena that are problematic; tensions between quantum theory and

26

general relativity. But is there any reason to think that positing fundamental intrinsic properties would help resolve these issues?

Option #2: One can embrace the view that there are no fundamental intrinsic properties, that all fundamental properties are extrinsic. There are two ways one might do this. One straightforward way would be to embrace a causal structuralism, the view according to which there is nothing to properties over and above their causal/locational roles. Alternatively, one might adopt a quidditistic view of extrinsic properties, where there are at bottom only extrinsics, but these extrinsics have their own natures or quiddities (over and above or instead of their causal roles).21 Instead of a picture according to which all that exists are substances (bare particulars) exhibiting causal regularities, this quidditistic structuralism takes the substances to be instantiating relations possessing a robust enough nature to ground resemblances between objects that have them. This nature goes over and above the actual causal role the substance occupies. So, on this view, though not according to causal structuralism, it would be possible for an extrinsic property to play a different causal role in a different possible world giving substances that have it different causal powers than it actually does. Either way, whether one accepts causal or quidditistic structuralism, one can accept strong physicalism with the optimistic premise that physical science is indeed on the right track. But one will not then be saddled with Humility, since there are no nature-revealing intrinsic properties to be left unknown.22

21

Thanks to Ted Sider for pointing out this option to me. One might ask whether, given my arguments in the preceding section, these structuralist options involve adopting more metaphysics than is licensed by physical science. Aren’t we problematically going beyond physical science in claiming that properties have essences of one sort or another? The short answer is no. For adopting causal or quidditistic structuralism does not involve adding to the list of properties provided by science, beyond what is needed to provide explanations and make predictions. It only involves making 22

27

Option #3: Finally, one can deny strong physicalism altogether. One may do this while accepting epistemic optimism by saying that physical science is only on the right track to giving a complete list of all of the physical properties. This leaves open the epistemic possibility of there being other properties we can know about not dependent on those physical properties. So although it may be the case that the properties of physical science are all extrinsic, the properties of other sciences and/or ordinary experience may be intrinsic, and we can come to know about them. David Chalmers, with his naturalistic dualism, seem to endorse such a picture accepting that all of the physical properties are extrinsic, but allowing the existence of other fundamental intrinsic properties which are given to us in conscious experience [1996: 153-5].23 This option does not need to embrace causal structuralism, but also need not endorse Humility since we can learn about intrinsic properties directly through experience. One issue with this approach however is that although one may be able to learn about some fundamental intrinsic properties, one can only learn about the intrinsic properties of one’s own experience. It seems we are still left without any knowledge of the intrinsic natures of things outside of our own mental states, and so this third approach is compatible with a more moderate Humility. This being the case, it is not an option that will appeal to one averse to any kind of Epistemic Humility.

6. Closing Remarks: Is There a Fundamental Level?

sense of the physical picture by explicating the modal features of the properties of physical science and those dependent upon them. 23 A similar picture was endorsed by Russell [1927] in his neutral monism phase.

28

In closing one might ask if we are indeed justified in assuming that there is fundamental level of physical science to be discovered – one which might turn out to be exhausted by instantiations of extrinsic properties. After all, one might think that if there is no fundamental level, then there is no problem about science’s tendency to dissolve into extrinsicness. It seems that it is only if there is a bottom level of reality that we have an issue about perceived bottom-level extrinsicality suggesting that the world is extrinsic through and through (modulo the instantiation of any merely derivative intrinsic properties). When we lose the fundamentality hypothesis, we might also lose any justification for epistemic optimism. For, if physical science can never in principle be complete, for every level described there is another deeper level not even touched upon, then we may no longer have any reason to believe that the properties at levels way below the ones we know about are anything like the ones physics talks about today. Then it might be the case that at levels way below those we are able to describe today, there are levels of intrinsic properties to be discovered. Still, even if we believe there is no fundamental level, we may still be epistemic optimists. Consider the following words of Richard Feynman: What will happen ultimately? We are going along guessing the laws; how many laws are there to guess? I do not know. Some of my colleagues say that this fundamental aspect of our science will go on; but I think there will certainly not be perpetual novelty, say for a thousand years. This thing cannot keep on going so that we are always going to discover more and more new laws. If we do, it will become boring that there are so many levels one underneath the other. It seems to me that what can happen in the future is either that all the laws become known …

29

or it may happen that experiments get harder and harder to make … so that you get 99.9 per cent of the phenomena, but there is always some phenomena which has just been discovered … and as soon as you have explanation of that one there is always another one, and it gets slower and slower and more and more uninteresting. [Feynman 1965: 172] Jonathan Schaffer describes a similar possibility in his “Is There a Fundamental Level?” [2003: 510]. The idea is that even if there is no fundamental level of reality, at some point explanations may get uninteresting. In this way, physical science could be complete even though it did not strictly cover all of the phenomena, since it did cover all of the interesting phenomena. Following up on this suggestion, since it seems that current physical science is able to explain much of what we come across in the world (perhaps not 99 per cent of the phenomena, but close enough), it seems fair to assume that either physicists are on the right track to describing the fundamental level, or at least on the right track to describing the level below which things stop being interesting. Either way, physicists are on the right track to what a complete physical theory will look like, and so we should not doubt epistemic optimism. Thus, the possibility that there is no fundamental reality does not by itself undermine the argument for epistemic Humility. And so we still have to deal with the three options left in its wake.24

24

Thanks to Allan Hazlett, Jaegwon Kim, Rae Langton, Rebekah Rice, Ted Sider, Jim Van Cleve, Brian Weatherson, and Nick Zangwill for helpful discussion.

30

References Armstrong, David 1997. A World of States of Affairs, Cambridge: Cambridge University Press. Armstrong, David 1968. A Materialist Theory of Mind, London: Routledge and Kegan Paul. Chalmers, David 1996. The Conscious Mind, Oxford: Oxford University Press. Crane, Tim and D.H. Mellor 1990. There is No Question of Physicalism, Mind 99: 185206. Dunn, Michael 1990. Relevant Predication 2: Intrinsic Properties and Internal Relations, Philosophical Studies 60: 177-206. Feynman, Richard 1965. The Character of Physical Law, Cambridge, MA: MIT Press. Hawthorne, John 2001. Causal Structuralism, Philosophical Perspectives 15: 361-78. Humberstone, I.L. 1996. Intrinsic/Extrinsic, Synthese 108: 205-67. Jackson, Frank 1998. From Metaphysics to Ethics: A defence of conceptual analysis, Oxford: Oxford University Press. Johnston, Mark 1996. Is the External World Invisible?, in Perception, ed. E. Villanueva, Ridgeview: Atascadero. Kim, Jaegwon 1998. Mind in a Physical World, Cambridge, MA: MIT Press. Kim, Jaegwon 1993. Concepts of Supervenience, in Supervenience and Mind, Cambridge: Cambridge University Press. Langton, Rae 2004. Elusive Knowledge of Things in Themselves, Australasian Journal of Philosophy 82: 129-36. Langton, Rae 1998. Kantian Humility, Oxford: Oxford University Press. Langton, Rae and David Lewis 1998. Defining ‘intrinsic’, Philosophy and Phenomenological Research 58: 333-45. Lewis, David 1986. On the Plurality of Worlds, Oxford: Blackwell. Lewis, David 1983. Extrinsic Properties, Philosophical Studies, 44: 197-200.

31

Lewis, David 1999 (1983). New Work for a Theory of Universals, in Papers in Metaphysics and Epistemology, Cambridge: Cambridge University Press. Lewis, David forthcoming. Ramseyan Humility. Pettit, Philip 1993. A Definition of Physicalism, Analysis 53: 213-23. Prior, Elizabeth, Robert Pargetter, and Frank Jackson 1982. Three Theses about Dispositions, American Philosophical Quarterly 19: 251-56. Quine, W.V.O. 1953. On What There Is, in From a Logical Point of View, Cambridge, MA: Harvard University Press. Russell, Bertrand 1927. The Analysis of Matter, London: Kegan Paul. Schaffer, Jonathan forthcoming. Quidditistic Knowledge, Philosophical Studies. Schaffer, Jonathan 2003. Is There a Fundamental Level? Nous 37: 498-517. Stoljar, Daniel 2001. Physicalism, entry in Stanford Online Encyclopedia of Philosophy, http://plato.stanford.edu/entries/physicalism/. Weatherson, Brian 2002. Intrinsic vs. Extrinsic Properties, entry in Stanford Online Encyclopedia of Philosophy, http://plato.stanford.edu/entries/intrinsic-extrinsic/.

32