Transcendental Arguments, Conceivability, and Global vs. Local Skepticism Moti Mizrahi Florida Institute of Technology Abstract: In this paper, I argue that, if transcendental arguments are to proceed from premises that are acceptable to the skeptic, the Transcendental Premise, according to which "X is a metaphysically necessary condition for the possibility of Y," must be grounded in considerations of conceivability and possibility. More explicitly, the Transcendental Premise is based on what Szabó Gendler and Hawthorne (2002, p. 2) call the "conceivability-possibility (or inconceivability-impossibility) move." This "inconceivability-impossibility" move, however, is a problematic argumentative move when advancing transcendental arguments for the following reasons. First, from "S cannot conceive of P" it doesn't necessarily follow that P is inconceivable. Second, from "P is inconceivable" it doesn't necessarily follow that P is metaphysically impossible. Third, rather than block skeptical doubts, the conceivabilitypossibility (or inconceivability-impossibility) move introduces skeptical doubts. For these reasons, transcendental arguments fail to deliver on their promise to overcome skeptical doubts. Keywords: conceivability; inconceivability; metaphysical necessity; metaphysical possibility; skepticism; transcendental argument 1. Introduction Stern (2013) identifies the following key features of transcendental arguments: (A) Transcendental arguments are anti-skeptical, which is why they must begin from a starting point that the skeptic can be expected to accept. In other words, "the point of transcendental arguments in general is an anti-skeptical point" (Strawson 2008, p. 8).1 (B) Transcendental arguments involve a transcendental claim, i.e., that X is a necessary condition for the possibility of Y, where the necessity and possibility in question are taken to be metaphysical, not logical or nomological. As Cassam (2007, pp. 54-55) points out, transcendental arguments are ineffective insofar as explaining how X is possible is concerned, but only insofar as showing that X is necessary for the possibility of Y is concerned. As far as (A) is concerned, Stern (2003) writes: there are clear dialectical advantages to beginning with something that even the sceptic will grant us as a starting point (such as subjective experience), whereas he may question the existence of reality conceived of in more objective terms. It is largely for this 1 See also Stroud (1968). 2 dialectical reason, therefore, that contemporary transcendental arguments follow Kant in focusing on the necessary conditions of experience, language, belief, intentionality, and so on, where the conditioned is something the sceptic himself is prepared to assume at the outset (Stern 2003, p. 4). That is, to be effective arguments against the skeptic, transcendental arguments must assume as premises claims that the skeptic is prepared to accept, such as claims about subjective experience. Furthermore: [Transcendental arguments] set out to show that something the sceptic takes for granted as a possibility (for example, that we have direct access to our inner states but no direct access to the external world, or beliefs but no reliable belief-forming methods) must be abandoned, as the one is in fact impossible without the other, for reasons he has overlooked (for example, that inner states alone cannot provide the basis for timedetermination, or that beliefs by their nature must be generally true) (Stern 2003, p. 4). As far as (B) is concerned, Stern (2003) says that: [Transcendental] arguments involve a claim of a distinctive form: namely, that one thing (X) is a necessary condition for the possibility of something else (Y), so that (it is said) the latter cannot obtain without the former. In suggesting that X is a condition for Y in this way, this claim is supposed to be metaphysical and a priori, and not merely natural and a posteriori: that is, if Y cannot obtain without X, this is not just because certain natural laws governing the actual world and discoverable by the empirical sciences make this impossible (in the way that, for example, life cannot exist without oxygen), but because certain metaphysical constraints that can be established by reflection make X a condition for Y in every possible world (for example, existence is a condition for thought, as the former is metaphysically required in order to do or be anything at all (Stern 2003, p. 3; emphasis in original). Accordingly, transcendental arguments have the following logical structure (Stern 2007, p. 144): Experience Premise: We have certain experiences Y. Transcendental Premise: A metaphysically necessary condition for us having Y is the truth of X. Conclusion: X.2 For example, against the external-world skeptic who denies the possibility of knowledge about the external world,3 Putnam (1981, pp. 14-15) puts forth an argument that can be reconstructed as a transcendental argument as follows (Wright 1992): 1. I can think that I'm not a BIV. 2. In order to think that I'm not a BIV it must be the case that I'm not a BIV. Therefore, 3. I'm not a BIV. (Cf. Pritchard and Ranalli 2016.) 2 On whether or not transcendental arguments can be undogmatic, see Kuusela (2008). 3 For a discussion of external world skepticism, see Greco (2007). 3 Premise (1) in Putnam's argument is supposed to be a premise that the external-world skeptic is prepared to accept, namely, that one can experience the thought I'm not a BIV. Premise (2) in Putnam's argument is supposed to capture a metaphysical constraint on reference, which stems from Putnam's causal theory of reference, according to which reference is partly fixed by context and causal history, which is why it is metaphysically impossible, on Putnam's view, to refer to something without being acquainted with it. From premises (1) and (2), then, (3) is supposed to follow, since Putnam's metaphysical constraint on reference doesn't seem to hold in the case of BIVs.4 Similarly, Descartes' Cogito argument can be construed as a transcendental argument against external-world skepticism as follows: 1. I can think that I'm thinking. 2. In order to think that I'm thinking I must exist. Therefore, 3. I exist. Again, premise (1) in Descartes' Cogito argument is supposed to be a premise that the externalworld skeptic is prepared to accept, namely, that one can experience the thought I'm thinking. Premise (2) in Descartes' Cogito argument is supposed to capture a metaphysical constraint on thinking, i.e., that it is metaphysically necessary to exist as a thinker in order to think. From premises (1) and (2), then, (3) is supposed to follow, since Descartes' metaphysical constraint on thinking does seem to hold in this case.5 In what follows, I argue that transcendental arguments cannot accomplish both (A) and (B) at the same time. More explicitly, I argue that, insofar as they rely on a transcendental premise concerning metaphysical possibilities, namely, the Transcendental Premise, transcendental arguments cannot be effective anti-skeptical arguments, for they depend on a move that introduces rather than blocks skeptical doubts. I will sketch three arguments in support of this claim. These arguments will stem from what I take to be the problematic argumentative move at the core of transcendental arguments, namely, what Szabó Gendler and Hawthorne (2002, p. 2) call the "conceivability-possibility (or inconceivability-impossibility) move."6 2. The conceivability-possibility (or inconceivability-impossibility) move To see the problem that I think transcendental arguments suffer from, consider the second premise of the transcendental argument schema sketched above, according to which "X is a metaphysically necessary condition for the possibility of Y." For this premise to be acceptable to the skeptic, as (A) dictates, it must be based on considerations that a skeptic would accept. For instance, in the case of Putnam's argument against the external-world skeptic, the second premise, according to which one must be acquainted with BIVs in order to refer to such things, is grounded in Putnam's causal theory of reference. But, surely, the external-world skeptic would 4 For a critique of Putnam's transcendental argument, see Brueckner (2010, pp. 93-94). See also Pritchard and Ranalli (2016) for discussion. 5 On Descartes' Cogito argument as a "performative transcendental argument," see Bardon (2005). 6 On other objections to transcendental arguments, see Stern 2004, chapter 2. 4 not find Putnam's theory of reference acceptable at all, since she thinks that there is no way to know that there is even an external world to refer to in the first place. So what else could Putnam appeal to in order to justify the second premise of his argument in a way that would be acceptable to the external-world skeptic? As an anonymous reviewer points out, it is important to note that Putnam advances other considerations in support of the causal theory of reference. For instance, by invoking the notion of "the linguistic division of labour" (Putnam 1975, pp. 227-228), and using examples like the one about 'elm' and 'beech', Putnam argues that we can refer to these trees, which is taken for granted, even if we are not experts. As Devitt and Sterelny (1999, p. 88) put it, the "causal theory lightens the epistemic burden."7 So the charge against Putnam's transcendental argument from BIVs cannot be that all inferences ultimately rest on considerations of conceivability and/or inconceivability; otherwise, the same charge could be leveled against the external-world skeptic as well (as we shall soon see). Rather, the charge against Putnam's transcendental argument from BIVs, from the point of view of the external-world skeptic, is that Putnam's argument invokes the notion of reference, and the notion of reference, in turn, presupposes links (on Putnam's view, causal links) between thought and reality. As Reimer and Michaelson (2016) explain: thinking you are a brain in a vat requires causal links to things which, if you were a brain in a vat, wouldn't exist. These are the sorts of causal links between thought and reality that would make thinking you are a brain in a vat possible in the first place. So you can't have such thoughts, if those thoughts are true. You can in fact have such thoughts, so they must not be true (emphasis added). But of course, it is precisely such links between thought and reality (or the external world) that the skeptic argues are beyond our ken. In other words, insofar as it invokes Putnam's causal theory of reference, Putnam's transcendental argument from BIVs presupposes that we are connected to the external world through thought, which is precisely what the external-world skeptic denies. After all, "How can something inside the head refer to something outside the head?" (Devitt 1990, p. 91; Putnam 1981, pp. 1-21) Similarly, in the case of Descartes' Cogito argument, the second premise, according to which I must exist in order to think, is grounded in Descartes' notion of what the "I" is, namely, a thinking thing. As Gassendi points out in his objections to Descartes' Mediations, however, Descartes cannot assume that there is a particular thinking subject, a thinker (or, as Descartes puts it a "thinking thing") without begging the question against the skeptic. For, as Fisher (2014) explains: [The] recognition that one has a set of thoughts does not imply that one is a particular thinker or another. Were we to move from the observation that there is thinking occurring to the attribution of this thinking to a particular agent, we would simply assume what we set out to prove, namely, that there exists a particular person endowed with the capacity for thought. So what else could Descartes appeal to in order to justify the second premise of his argument in a way that would be acceptable to the skeptic? 7 For a more recent discussion of "reference borrowing," see Devitt (2006, pp. 138-141). 5 Since the second premise of a transcendental argument, like Putnam's argument from reference to BIVs and Descartes' Cogito argument, is a transcendental claim about metaphysical necessities, the only considerations one can appeal to, I submit, are considerations of conceivability. After all, even skeptics appeal to considerations of conceivability when they argue from skeptical hypotheses, such as the BIV hypothesis. Indeed, it is common practice among philosophers to appeal to considerations of conceivability in order to support claims about possibility. For example, Chalmers (2010, pp. 142) argues from the conceivability of philosophical zombies to the metaphysical possibility of such beings.8 If this is correct, then, for any transcendental argument, the Transcendental Premise, according to which "X is a metaphysically necessary condition for Y," must be grounded in considerations of conceivability, more precisely, that Y is inconceivable without X or that Y is conceivable only if X. According to Szabó Gendler and Hawthorne (2002, p. 5-6), many philosophers hold that "our ability to conceive of a scenario where P obtains is reckoned as constituting at least prima-facie reason for supposing that P is metaphysically possible." The notion of metaphysical possibility is taken to be primitive, according to Szabó Gendler and Hawthorne (2002, p. 4), and is simply glossed as "how things might have been," or "how God might have made things," or "the ways it is possible for things to be" (cf. Chalmers 2002, p. 146). The relevant notion of conceivability here is the one Chalmers calls "primary conceivability." According to Chalmers (2002, p. 157), P "is primarily conceivable (or epistemically conceivable) when it is conceivable that [P] is actually the case." To use Chalmers' (2002, p. 158) example, "'Hesperus is not Phosphorus' is primarily [i.e., considered as actual] positively conceivable."9 More importantly, for present purposes, according to Szabó Gendler and Hawthorne (2002, p. 2), "from the fact that we are (or are not) able to depict to ourselves a scenario in which thus-and-such obtains, we take ourselves to have learned something about whether thus-and-such could (or could not) obtain." They call this the "conceivability-possibility (or inconceivabilityimpossibility) move." This move, I submit, is what grounds the Transcendental Premise of a transcendental argument. In the case of Putnam's argument against the external-world skeptic, for example, it is supposed to be inconceivable that one can refer to BIVs without being aquatinted with such things, and thus that one is not a BIV. Likewise, in the case of Descartes' Cogito argument, it is supposed to be inconceivable that one can think without existing, since one is a thinking thing, and thus it is metaphysically impossible for one to be a thinking thing without existing. If this is correct, then the key question for present purposes is whether or not the "conceivability-possibility (or inconceivability-impossibility) move" can be deployed successfully in order to advance transcendental arguments against skepticism; keeping in mind that transcendental arguments are supposed to have features (A) and (B) in order to be successful anti-skeptical arguments. I think that the conceivability-possibility (or inconceivabilityimpossibility) move cannot be deployed successfully in this way. I will now discuss in some detail three reasons why that is the case. 2a. "S cannot conceive of P" doesn't entail "P is inconceivable" 8 See also Chalmers (2002). 9 Cf. Yablo's (1993) notion of conceivabilityep. 6 First, there is a distinction to be made between P being (primarily, positively) inconceivable and failure to conceive of a scenario where P obtains. Presumably, many pre-nineteenth century physicists would have had a hard time conceiving of a world where, were it the actual world, it would be true that our universe is a four-dimensional space-time continuum, which is something that we now think we can conceive of. The point, then, is that failure to conceive of a scenario where P obtains is not the same as P being inconceivable, and hence metaphysically impossible. If so, then we need a good reason to think that, if we fail to conceive of a scenario where P obtains, then that shows-or is at least a strong reason to believe- that P is indeed inconceivable. Even if we do have such a reason, though see Mizrahi and Morrow (2015), this means that there is no straightforward entailment between "P is inconceivable" to "P is metaphysically impossible," given that one's failure to conceive of a scenario where P obtains is not conclusive evidence that P is indeed inconceivable, as plenty of other historical examples show. If this is correct, then the conceivability-possibility (or inconceivability-impossibility) move cannot ground the Transcendental Premise of a transcendental argument, according to which "X is a metaphysically necessary condition for Y," since the fact that one fails to conceive of a possible world in which P obtains is not conclusive evidence that P is indeed inconceivable. But this means that Y may not be a metaphysically necessary condition for the truth of X after all. For example, Putnam finds it hard to conceive of a world in which one can refer to BIVs without being aquatinted with BIVs. As was the case for nineteenth-century physicists, this may simply be a failure on Putnam's part, not a sure sign that referring to BIVs without being acquainted with BIVs is inconceivable. Similarly, Descartes finds it hard to conceive of a world in which there is thinking without a particular thinker. As was the case for nineteenth-century physicists, this may simply be a failure on Descartes' part, not a sure sign that there being thinking without there being a particular thinker is inconceivable. 2b. "P is inconceivable" doesn't entail "P is metaphysically impossible" Second, since we are not creatures of unlimited cognitive abilities, it is reasonable to think that there are certain things that we simply cannot conceive of just as there are certain things that are conceptually beyond dogs and ants. Perhaps there are extra-terrestrial intelligent beings with modal powers that are superior to ours such that they can conceive of many more things than we can. If there are such creatures, then they would deem conceivable, and hence metaphysically possible, what we deem inconceivable, and hence metaphysically impossible. But this means that there is no straightforward entailment between "P is inconceivable" and "P is metaphysically impossible," given that there are some things that we cannot conceive of, on account of our limited cognitive capacities, just as there are some things that dogs and ants cannot conceive of. If this is correct, then, again, the conceivability-possibility (or inconceivabilityimpossibility) move cannot ground the Transcendental Premise of a transcendental argument, since the fact that one fails to conceive of a possible world in which P obtains is not conclusive evidence that P is indeed inconceivable. But, again, this means that Y may not be a metaphysically necessary condition for the truth of X after all. For example, perhaps extraterrestrial intelligent beings with modal powers superior to those of Putnam would be able to conceive of a world in which one can refer to BIVs without being aquatinted with BIVs, just as 7 Putnam can conceive of things that ants cannot. Again, this may simply be a limitation on Putnam's part, in virtue of being a creature of limited cognitive abilities, not a sure sign that referring to BIVs without being acquainted with BIVs is inconceivable. Similarly, perhaps extra-terrestrial intelligent beings with modal powers superior to those of Descartes would be able to conceive of a world in which there is thinking without a particular thinker, just as Descartes can conceive of things that ants cannot. Again, this may simply be a limitation on Descartes' part, in virtue of being a creature of limited cognitive abilities, not a sure sign that there being thinking without there being a particular thinker is inconceivable. 2c. The floodgates of skeptical doubts Third, rather than block skeptical doubts, which is what transcendental arguments are supposed to do, as (A) dictates, the conceivability-possibility (or inconceivability-impossibility) move opens the floodgates of skeptical doubts. That is to say, it allows the skeptic to raise skeptical doubts that transcendental arguments were meant to overcome. I will mention two kinds of skeptical doubt that the conceivability-possibility (or inconceivability-impossibility) move allows the skeptic to raise: global skeptical doubts and local skeptical doubts.10 As far as global skeptical doubts are concerned, the conceivability-possibility (or inconceivability-impossibility) move allows the skeptic to argue from skeptical hypotheses. Indeed, the familiar skeptical arguments from skeptical hypotheses, such as the deceiving demon (Schaffer 2010), dreaming (Brown 2009), and the BIV hypotheses, proceed on the assumption that such skeptical hypotheses are conceivable. That is to say, one can conceive of a world in which one is a handless brain in a vat and that this world is the actual world. According to Greco (2007, p. 625), arguments for external-world skepticism from skeptical hypotheses generally proceed as follows: SA Let o be some ordinary proposition about the external world, such as that I have two hands, and let h be a proposition describing some skeptical hypothesis, such as that I am a handless brain in a vat. 1. I know that o only if I know that ¬h. 2. But I don't know that ¬h. Therefore, 3. I don't know that o. The conceivability-possibility (or inconceivability-impossibility) move, then, allows the skeptic to ground the first premise of SA in considerations of conceivability. That is to say, as long as it is conceivable that one is a handless brain in a vat (or that one is being deceived by a malicious demon), premise (1) of SA holds, and the skeptic can then conclude that one does not know the truth of any ordinary proposition about the external world. 10 On global and local skepticism, see Maitzen (2006). Maitzen argues that local skepticism cannot stay local. But his argument proceeds from the case of ethical skepticism (or nihilism) alone. 8 As far as local skeptical doubts are concerned, the conceivability-possibility (or inconceivability-impossibility) move allows the skeptic to raise specific doubts about scientific claims to knowledge. For example, "the generally accepted big bang theory holds that the observable universe emerged from an explosion some ten to twenty billion years ago [and nonetheless] that all the matter in the universe was present from the start" (Guth 1997, p. 2). But how can that be? After all, "Nothing can be created from nothing" (Guth 1997, p. 2). That something can come from nothing seems inconceivable. If it is, then the skeptic can argue as follows: 1. It is inconceivable that the universe came into existence from nothing. 2. If it is inconceivable that P, then it is impossible that P. Therefore, 3. It is impossible that the universe came into existence from nothing. Now, whatever is impossible cannot be actual. So, from (3), it follows that it is not the case that our universe came into existence from nothing. And that, in turn, means that the Big Band model is incorrect, since it "assigns a finite age to the universe" (Guth 1997, p. 335), and thus a moment in which the universe was created from nothing.11 Accordingly, the conceivability-possibility (or inconceivability-impossibility) move gives the skeptic a tool for raising local doubts about scientific claims to knowledge. Here is another example. According to "the best theory we have of nature [whose] predictions have been verified over an immense range of phenomena" (Stenholm 2002, p. 186), namely, Quantum Mechanics, a subatomic particle, such as an electron, can be in a superposition of quantum states, e.g., one and the same particle can pass through two slits at the same time. But how can that be? That one and same particle can pass through two slits at the same time seems inconceivable. If it is, then the skeptic can argue as follows: 1. It is inconceivable that a particle can be in a superposition of quantum states. 2. If it is inconceivable that P, then it is impossible that P. Therefore, 3. It is impossible that a particle can be in a superposition of quantum states. Again, whatever is impossible cannot be actual. So, from (3), it follows that it is not the case that a particle can be in a superposition of quantum states. That, in turn, means that quantum mechanics is incorrect, since the principle of superposition is a fundamental principle of Quantum Mechanics, and it implies that "a particle in one quantum state is also simultaneously in other quantum states" (Phillips 2003, p. 52).12 If we grant the skeptic the conceivability-possibility (or inconceivability-impossibility) move, then, she can use it to raise global as well as local skeptical doubts. This result, I submit, may be particularly problematic for some friends of the move who also turn to science either for empirical confirmation of their views or for making their views consistent with the relevant science. For instance, Chalmers, who is a key proponent of the conceivability-possibility (or inconceivability-impossibility) move, as we have seen, also talks about the "science of 11 See also Albert's (2012) review of Krauss' book, A Universe from Nothing (2012), in The New York Times. 12 For more on superposition, see Albert (1992, pp. 1-16). 9 consciousness" (as opposed to the philosophy of consciousness), thinks that "the prospects for a science of consciousness are reasonably bright" (Chalmers 2010, p. 52), appeals to scientific evidence (Chalmers 2010, p. 48), and talks about "the world as revealed by contemporary science" (Chalmers 2010, xxv). If the aforementioned considerations are correct, however, then something's got to give. That is to say, Chalmers cannot appeal to the conceivability-possibility (or inconceivabilityimpossibility) move when theorizing about consciousness (see, for example, his famous zombie argument in Chalmers 2010, pp. 141-206) while, at the same time, appealing to scientific theories that have inconceivable consequences. Some of our best scientific theories, such as the Big Bang model and Quantum Mechanics, tell us things that we find inconceivable, such as the universe coming into existence from nothing and particles being in several quantum states simultaneously. Anyone who endorses the conceivability-possibility (or inconceivabilityimpossibility) move, then, would have to conclude that these scientific theories must be incorrect, since they have inconceivable consequences. At this point, it might be objected that transcendental arguments are supposed to uncover problems with skeptical hypotheses such that those hypotheses become impossible. Presumably, this is what Kant's Refutation of Idealism is supposed to do.13 That is, Kant's Refutation of Idealism is supposed to demonstrate the "theorem" that "The mere, but empirically determined, consciousness of my own existence proves the existence of objects in space outside me" (Kant 1998, p. 327; B 275). In the Critique of Pure Reason (B 275-276), Kant writes: I am conscious of my existence as determined in time. All time-determination presupposes something persistent in perception. This persistent thing, however, cannot be something in me, since my own existence in time can first be determined only through this persistent thing. [According to the revised preface (B xxxix), this sentence is to be replaced by the following: "This persistent thing, however, cannot be an intuition in me. For all grounds of determination of my existence that can be encountered in me are representations, and as such require something persistent that is distinct even from them, in relation to which their change, thus my existence in the time in which they change, can be determined."] Thus the perception of this persistent thing is possible only through a thing outside me and not through the mere representation of a thing outside me. Consequently, the determination of my existence in time is possible only by means of the existence of actual things that I perceive outside myself (Kant 1998, p. 327). Since the aim of this paper is to assess whether or not transcendental arguments succeed in overcoming skeptical doubts, rather than engage in Kant scholarship, I will use for the sake of the present discussion a reconstruction of Kant's Refutation of Idealism that many Kant scholars seem to find satisfactory. This reconstruction is offered by Dicker (2004, pp. 194-211): (1``) I seem to be able to correctly determine the order in time of experiences of mine that did not (a) occur within a specious present, and that do not (b) belong to a remembered sequence of continuous experiences or (c) include a recollection of the sequence of all the earlier experiences within each of the later ones (original emphasis). 13 Many thanks to an anonymous reviewer for raising this objection. 10 (2``) When I remember two or more past experiences that are not of type (a)-(c), my recollection of those experiences does not itself reveal the order in which they seem to me to have occurred (emphasis added). (3``) If (2``), then I cannot correctly determine the order in which two or more past experiences of mine that are not of type (a)-(c) seem to me to have occurred just by recollecting them (emphasis added). (4``) I cannot correctly determine the order in which two or more past experiences of mine that are not of type (a)-(c) seem to me to have occurred just by recollecting them. [from (2``) and (3``)] (5``) If I cannot correctly determine the order in which two or more past experiences of mine that are not of type (a)-(c) seem to me to have occurred just by recollecting them, then I can seem to be able to correctly determine the order in time of two or more past experiences of mine that are not of type (a)-(c) only if I conceive some of my experiences as being caused by successive objective states of affairs that I perceive (emphasis added). (6``) I can seem to be able to correctly determine the order in time of two or more past experiences of mine that are not of type (a)-(c) only if I conceive some of my experiences as being caused by successive objective states of affairs that I perceive. [from (4``) and (5``)] (7``) I conceive some of my experiences as being caused by successive objective states of affairs that I perceive. [from (1``) and (6``)]14 As Dicker (2008, p. 105) points out, (7``) seems rather disappointing, "for it fails to say that I must conceive of my experiences as being caused by successive objective states of affairs that I perceive" (original emphasis). Dicker goes on to say that Kant's Refutation of Idealism does succeed in showing that "even if one is skeptical about knowledge of the order of one's own past experiences, as long as it is granted that one at least seems to be able to assign a determinate order to them, one must conceive of them as experiences of an objective world" (emphasis added). The Transcendental Premise in Dicker's reconstruction of Kant's Refutation of Idealism is premise (6``). For this premise to be acceptable to the skeptic, as (A) dictates, it must be based on considerations that the skeptic would accept. Note, however, that, as stated, Kant's Refutation of Idealism concerns what one seems to be able to do and what one's experiences are like. Surely, these are premises that are not acceptable to the skeptic. After all, skeptical hypotheses, such as BIV, are supposed to illustrate how "objective states of affairs" can be radically different from the way they seem or appear to us. Given this "distinction between 'appearance' and 'reality', between what things seem to be and what they are" (Russell 1912, p. 12), the skeptic can argue that there can be no knowledge about the external world because such "knowledge requires good inferences [from how things appear to how things are]" (Greco 2000, p. 104). Since "there is no good inference from how things appear to how things are" (Greco 2000, p. 86), it follows that there can be no knowledge of the external world. Similarly, Mizrahi (2015, p. 6) shows that the skeptic could argue as follows: for S to know that p, where p is a proposition 14 Cf. Allison (2004, p. 275-304), Stern (2008, pp. 272-273), and Pereboom (2014). 11 about the external world, such as 'I have hands', S must be able to distinguish between it being the case that p and it appearing to S as if p. Since S cannot distinguish the two, it follows that S doesn't know that p. Given the appearance/reality distinction, then, all that Kant's argument succeeds in showing is what our appearances are like, not what reality is like. So, rather than presuppose some link between appearances and reality, which the skeptic would not accept, what else could Kant appeal to in order to justify the Transcendental Premise of his Refutation of Idealism, namely, premise (6``) in Dicker's reconstruction, in a way that would be acceptable to the skeptic? Insofar as Kant's Refutation of Idealism is a transcendental argument, the Transcendental Premise of this argument, namely, (6``), must be grounded in considerations of conceivability and possibility, as I have argued above. In other words, it must be based on the conceivabilitypossibility (or inconceivability-impossibility) move. As I have argued above, however, the conceivability-possibility (or inconceivability-impossibility) move cannot ground the Transcendental Premise of a transcendental argument, according to which "X is a metaphysically necessary condition for Y," since the fact that one fails to conceive of a possible world in which P obtains is not conclusive evidence that P is indeed inconceivable. But this means that Y may not be a metaphysically necessary condition for the truth of X after all. In the case of Kant's Refutation of Idealism, Kant might find it hard to conceive of a world in which one can have self-conscious experiences without there being physical objects outside of one's mind (Brueckner 2010, p. 11). But this may simply be a failure on Kant's part, not a sure sign that selfconscious experience without physical objects is inconceivable. Indeed, a skeptical hypothesis, such as The Matrix, is supposed to be a scenario in which one can have self-conscious experiences of objects that do not exist. For instance, it might seem to one as if one is experiencing the flavor of a mouth-watering steak and the taste of red wine, but of course, in a computer simulation like The Matrix, there are not steaks and there is no red wine. I take Brueckner (2010, p. 11) to be raising somewhat similar concerns about Kant's Refutation of Idealism when he, too, says that the argument is "disappointing." Even "a successful Kantian transcendental argument," Brueckner (2010, p. 11) argues, "would not certify any of one's claims to know facts about particular physical objects." For, if one were a BIV, one would be in a scenario in which one could be caused to experience event A before event B, but also be caused to experience event B before event A. So, although one would experience either A before B or B before A, one could still end up having false conceptions about the temporal sequence of events A and B. Similarly, the Architect of The Matrix could easily make one experience events in some order other than the order in which they actually occurred, e.g., the experience of tasting a mouth-watering steak before the experience of savoring a glass of red wine, and vice versa. If this is correct, then Kant's Refutation of Idealism fails to show that skeptical hypotheses, such as BIV and The Matrix, are impossible. For such skeptical hypotheses to be impossible, they would have to be inconceivable, since the Transcendental Premise of a transcendental argument like Kant's Refutation of Idealism must be grounded in considerations of conceivability and possibility (i.e., the inconceivability-impossibility move) in order to be acceptable to the skeptic. Such considerations, however, cannot ground the Transcendental Premise because from "S cannot conceive of P" it doesn't necessarily follow that P is inconceivable, and from "P is inconceivable" it doesn't necessarily follow that P is 12 metaphysically impossible. Indeed, The Matrix is supposed to be a scenario in which one can have temporally ordered experiences of objects that do not exist. Moreover, perhaps extraterrestrial intelligent beings with modal powers superior to those of Kant would be able to conceive of a world in which one can have self-conscious experiences of physical objects that do not exist or successive events that do not obtain. Again, this may simply be a limitation on Kant's part, in virtue of being a creature of limited cognitive abilities, not a sure sign that "the existence of physical objects is a [necessary] condition for the possibility of self-conscious experience" (Brueckner 2010, p. 11). 3. Conclusion In this paper, I have argued that, if transcendental arguments are to proceed from premises that are acceptable to the skeptic, the Transcendental Premise, according to which "X is a metaphysically necessary condition for the possibility of Y," must be grounded in considerations of conceivability and possibility. More explicitly, the premise "X is a metaphysically necessary condition for the possibility of Y" is based on what Szabó Gendler and Hawthorne (2002, p. 2) call the "conceivability-possibility (or inconceivability-impossibility) move." This move, however, is a problematic argumentative move when advancing transcendental arguments for the following reasons. 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