Chalmers on the apriority of modal knowledge Christopher S. Hill David Chalmers’s book on consciousness (1996) has a number of admirable qualities – it is bold, imaginative, articulate, well informed, and in a number of places, enormously illuminating. It is also true, however, that several passages in the book have significant flaws. I discuss two of these passages in the present note. A main point of the book is to argue for property dualism – that is, for the claim that the intrinsic properties of conscious experiences are distinct from all physical and functional properties. Chalmers’s argument for this claim can be summarized as follows: ‘In order for the facts of consciousness to be reductively explainable in terms of physical and/or functional facts, it must be the case that it is logically impossible for there to be a world w such that (a) w is just like the actual world with respect to all physical and functional facts, but (b) w fails to contain all of the facts of consciousness that obtain in the actual world. Now it is epistemologically appropriate to test for logical possibility and logical impossibility by a priori methods, and in particular, it is appropriate to test for whether it is logically possible for there to be a world that meets conditions (a) and (b) by seeing whether one can conceive of such a world. When we apply this test, we find that it has a positive outcome. Thus, for example, we find that we can conceive of a world in which the physical and functional facts are the same as they are in the actual world but in which consciousness is altogether absent – a world in which there are physical/functional twins of all beings who possess consciousness in the actual world but in which those twins are zombies. It turns out, then, that it is logically possible for there to be a world that meets conditions (a) and (b), and by the same token, it turns out that the facts of consciousness are not reducible to physical and/ or functional facts. We can conclude from this that the properties in virtue of which states count as conscious experiences are distinct from physical and functional properties.’ It is clear that this argument for property dualism depends heavily on the claim that we have a priori access to logical possibility. In the present paper I examine two passages in which Chalmers appears to offer justifications for this view. The passages I focus on are not the only ones in the book that offer such justifications, and in fact Chalmers informs me that the passages in question are not the ones that he regards as making the strongest case for his view. Despite this disavowal by Chalmers, however, it seems to me to be important to subject the passages in question to critical scrutiny. Analysis 58.1, January 1998, pp. 20–26. © Christopher S. Hill
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Thus, as several conversations have made clear to me, the passages contribute to the reader’s impression that Chalmers’s views are multiply anchored, that is, to the impression that there are several independent arguments that provide support for his position.1 The first of the two passages I have in mind runs as follows: If a statement is logically possible or necessary according to its primary intension, the possibility or necessity is knowable a priori, at least in principle. Modality is not epistemically inaccessible: the possibility of a statement is a function of the intensions involved and the space of possible worlds, both of which are epistemically accessible in principle, and neither of which is dependent on a posteriori facts in this case. So matters of 1-possibility … are accessible from the armchair. (1996: 68) I will call the line of thought in this passage the accessibility argument. I will endeavour to show that it begs the question. In order to assess the accessibility argument, we must begin by taking note of Chalmers’s distinction between the primary intension of a term or concept and the secondary intension of that term or concept. Chalmers introduces the notion of a primary intension in the following passage: The primary intension of a concept is a function from worlds to extensions reflecting the way that actual-world reference is fixed. In a given world, it picks out what the referent of the concept would be if that world turned out to be actual. Take the concept ‘water.’ If the actual world turned out to have XYZ in its oceans and lakes, then ‘water’ would refer to XYZ, but given that it turns out to have H2O in the oceans and lakes, ‘water’ refers to H2O. So the primary intension of ‘water’ maps the XYZ world to XYZ, and the H2O world to H2O. At a rough approximation, we might say that the primary intension picks out the dominant, clear drinkable liquid in the oceans and lakes; or more briefly, that it picks out the watery stuff in a world. (1996: 57) In general, where T is a general term or a general concept, we can say that the primary intension of T is a function that maps each possible world w onto a class of objects in w, where the class consists of exactly those objects in w that have the properties that we invoke in fixing the reference of T in the actual world.2 Having introduced the notion of a primary intension, Chalmers goes on immediately to say that our grasp of a primary intension is a priori. Thus, he tells us that the primary intension of a term or a concept ‘is independent 1
Brian McLaughlin and I discuss another line of thought leading to Chalmers’s views about modal knowledge in Hill and McLaughlin, forthcoming.
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of empirical factors: the intension specifies how reference depends on the way the external world turns out, so it does not itself depend on how the external world turns out’. (1996: 57) The primary intension of a term or concept T is the ‘a priori aspect’ of the meaning of T. The notion of a secondary intension is explained as follows: The secondary intension of a concept such as ‘water’ is not determined a priori, as it depends on how things turn out in the actual world. But it still has a close relation to the primary intension above. In this case, the secondary intension is determined by first evaluating the primary intension at the actual world, and then rigidifying this evaluation so that the same sort of thing is picked out in all possible worlds. Given that the primary intension (‘watery stuff’) picks out H2O in the actual world, it follows from rigidification that the secondary intension picks out H2O in all possible worlds. (1996: 59) The difference between the primary intension of a term or concept and the secondary intension is ultimately a matter of epistemic access, that is, of how the intension is presented to us. When we assign a primary intension to a term, we pick the intension out in such a way that it is possible to have immediate, non-conditional knowledge of which intension is picked out – that is, in such a way that it is possible to have knowledge of which intension is picked out that does not depend in any way on a posteriori information. But when we assign a secondary intension to a term, the identity of the intension that is assigned is conditional on a posteriori facts. Chalmers’s views about the meanings of statements are closely related to his views about the meanings of terms. Thus, as in the case of terms, he thinks that statements have both primary and secondary meanings. [T]here are two sets of truth conditions associated with any statement. If we evaluate the terms in a statement according to their primary intensions, we arrive at the primary truth conditions of the statement; that is a set of … possible worlds in which the statement, evaluated according to the primary intensions of the terms therein, turns out to be true …. If instead we evaluate the terms involved according to their 2
What I say here concerning Chalmers’s views about the primary intensions of general terms also applies, mutatis mutandis, to his views about the primary intensions of singular terms. In explaining primary intensions in this way, I am prescinding from a feature of primary intensions that is irrelevant to the issues addressed in the present note. Instead of seeing primary intensions as functions from worlds to extensions, as I have explained them here, Chalmers actually views them as functions from centred worlds to extensions, where a centred world is a pair consisting of a possible world and another pair, the constituents of which are an observer and a time. See, e.g., 1996: 60 .
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secondary intensions, we arrive at the more familiar secondary truth conditions. These conditions specify the truth-value of a statement in counterfactual worlds, given that the actual world has turned out as it did. (1996: 63) Thus, the primary intension of a statement S is a condition C such that (a) the question of whether S is true at a possible world is determined by whether the world satisfies C, and (b) C is determined by the primary intensions of the terms in S. It follows from (b) that our grasp of C is does not depend in any way on knowledge of a posteriori facts. The secondary intension of S is also a truth condition, but it is given to us only by description, where the referent of the description depends on what empirical facts happen to obtain in the actual world. One final explanatory remark. In the last sentence of passage I quoted first, Chalmers uses the expression ‘1-possibility’. As he understands it, this technical term is equivalent with the expression ‘possible according to the primary intension of the statement,’ and by the same token, equivalent with the expression ‘true at some possible world according to the primary intension of the statement’. (1996: 65) We are now in a position to assess the accessibility argument. Pared to essentials, the conclusion of the argument is (1): (1) If a statement is logically possible according to its primary intension, this possibility is knowable a priori. This conclusion is represented as following from three premisses: (2) Whether a statement is logically possible according to its primary intension is a function of the primary intension of the statement and of the space of possible worlds. (3) Our epistemic access to the primary intension of a statement is independent of a posteriori facts. (4) Our epistemic access to the space of possible worlds is independent of a posteriori facts. Premiss (2) is clearly correct. To say that a statement is logically possible according to its primary intension is just to say that there is a logically possible world that satisfies the primary truth condition of the statement. It is trivially true that the question of whether there is a logically possible world that satisfies a given truth condition is a function of the truth condition and of the space of possible worlds. Further, given the foregoing characterization of primary intensions, it is clear that (3) is correct. A primary intension is by definition an intension that we can grasp independently of a posteriori facts. On the other hand, it is far from clear that premiss (4) is correct. Moreover, on reflection it becomes evident that, on
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it most natural interpretation, (4) is a disguised version of the very proposition that the accessibility argument purports to establish! To see that this objection to the accessibility argument is correct, observe first that it is pretty clear that asserting (4) is equivalent to asserting (5): (5)
For any statement S, if it is within our power to know whether it is logically possible for S to be true, then it is within our power to know a priori whether it is logically possible for S to be true.
Now (5) can be understood in two ways. It can be understood as an equivalent of (5*): (5*) For any statement S, if it is within our power to know whether it is logically possible for S to be true according to its primary intension, then it is within our power to know a priori whether it is logically possible for S to be true according to its primary intension. (5) can also be understood as an equivalent of (5**): (5**) For any statement S, if it is within our power to know whether it is logically possible for S to be true according to its secondary intension, then it is within our power to know a priori whether it is logically possible for S to be true according to its secondary intension. Interpretation (5**) is ruled out because, as Chalmers emphasizes, when we are concerned with the secondary intension of a statement, our knowledge of the modal status of the statement is a posteriori. Thus, proposition (5*) is the only admissible interpretation of (4). But it is obvious that (5*) is tantamount to the intended conclusion of the argument (i.e., to (1)). So the accessibility argument begs the question. This brings us to the second of the two passages I wish to discuss. It runs as follows: And conversely, if a statement is 1-necessary, then it will be true no matter how the actual world turns out, so it will be true a priori. In most such cases, the statement’s truth will be knowable by us a priori; the exceptions may be certain mathematical statements whose truth we cannot determine, and certain statements that are so complex that we cannot comprehend them. Even in these cases, it seems reasonable to say that they are knowable a priori at least in principle, although they are beyond our limited cognitive capacity. (1996: 69) To understand this passage, we need only observe that Chalmers explains the notion of 1-necessity by saying that a statement is 1-necessary if it is true at all possible worlds according to its primary intension. (1996: 65)
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The quoted passage has two main components. The first component, which consists of the initial sentence, presents an argument for the view we are considering – the view that logical necessity according to primary intension can be grasped a priori. The second component qualifies this view. I will focus exclusively here on the argument. Once I have stated my objection to it, it will be apparent that Chalmers’s qualifications have no bearing on the question of whether the argument should be accepted. The argument may be paraphrased as follows: (6) Suppose that the statement S is true in all possible worlds according to its primary intension. (7) By this assumption, S will be true according to its primary intension no matter how the actual world turns out. (8) Hence, it can be seen a priori that S is true according to its primary intension. It is obvious that (7) follows from (6), so we need to concern ourselves only with the question of whether (8) follows from (7). To see that the answer to this question is negative, it helps to observe that (7) can be reformulated as (9): (9) By assumption, no matter which statements turn out to be true in the actual world, it will be the case that S is true in the actual world according to its primary intension. Since (7) is equivalent with (9), the inference from (7) to (8) stands or falls with the inference from (9) to (8). But it is clear that (9) has no tendency to support (8), for it is clear that (9) and (8) are concerned with different issues. (9) tells us only that a certain statement is true in the actual world; it makes no claims about our ability to apprehend the truth of the statement. (8), on the other hand, is a claim about what can be seen to be true, and in particular, a claim about what can be seen to be true independently of experience. In other words, while (9) is content to claim that a certain statement is true, (8) makes a claim about the existence and power of certain cognitive capacities. Thus, when the argument is subjected to careful scrutiny, it quickly becomes apparent that it is fallacious. To what, then, does it owe its initial plausibility? Part of the answer is surely that (9) is easily confused with (10): (10 By assumption, no matter which statements turn out to be true in the actual world, S will turn out to be true in the actual world according to its primary intension. Because it claims that S will turn out to be true, (10) makes a claim about
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cognitive capacities, and it is therefore capable of giving the impression that it is pertinent to (8). Can we save Chalmers’s argument by replacing (9) with (10) in our reconstruction of it? No. Thus, among other things, reflection shows that (10) is not an adequate paraphrase of (7). To conclude: I have criticized two passages which appear to offer support for Chalmers’s view that if a statement is logically necessary when it is interpreted in accordance with its primary intension, then it is possible for us to know a priori that it is logically necessary. I have not thereby established that Chalmers’s view is unsupported, for as I remarked at the outset, the book contains passages which suggest alternative reasons for holding the view. Moreover, it must be acknowledged that philosophers who are opposed to property dualism must do more than criticize Chalmers’s arguments. Thus, since Chalmers is clearly right to maintain that it is within our power to conceive of zombies, and since anyone who is not a sceptic about modal knowledge will grant that conceivability is an adequate test for logical possibility and logical necessity in some cases, those of us who wish to deny that zombies are logically possible are obliged to explain exactly why a test that works well enough in some cases is unreliable in others. Until this obligation and certain related obligations are discharged, Chalmers and other advocates of property dualism will continue to think that there must be something right about the enterprise of defending their views by Cartesian modal arguments.3 University of Arkansas Fayetteville, AR 72701, USA
[email protected] References Chalmers, D. J. 1996. The Conscious Mind. Oxford: Oxford University Press. Hill, C. S. 1997. Imaginability, conceivability, possibility, and the mind-body problem. Philosophical Studies 87: 61–85. Hill, C. S and B. McLaughlin. Forthcoming. There are fewer things in reality than are dreamt of in Chalmers’s philosophy. Philosophy and Phenomenological Research.
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I offer skeletal solutions to the problems described in this paragraph in Hill 1997. See also Hill and McLaughlin, forthcoming. I have benefited significantly from conversations and correspondence with David Chalmers, and also from Brian McLaughlin’s comments on an earlier version of the present note.
