Abstract
Some philosophers argue that we are justified in rejecting skepticism because it is explanatorily inferior to more commonsense hypotheses about the world. Focusing on the work of Jonathan Vogel, I show that this “abductivist” or “inference to the best explanation” response rests on an impoverished explanatory framework which ignores the explanatory gap between an object's having certain properties and its appearing to have those properties. Once this gap is appreciated, I argue, the abductivist strategy is defeated.
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Notes
This is in contrast to what may be called universal skepticism, which calls into doubt even cogito arguments. Schaffer (2010) contends that there is a genuine philosophical argument for such a position.
I discuss just which principles of reasoning we are allowed in Sect. 2.
This terminology and classificatory structure closely follows Vogel’s (2009).
In this section, I am adopting an abductivist strategy for assessing the plausibility of various skeptical hypotheses. While this may seem odd, given that my purpose in this paper is to argue against abductivism, I believe that my use here is legitimate. I actually believe that abductivism successfully dismisses certain skeptical hypotheses (for the reasons I set out in this section). What I deny is that it is a successful strategy for refuting Cartesian skepticism in general. Doing this would require being able to show that all skeptical hypotheses are explanatorily inferior to the real world hypothesis, and I believe the abductivist strategy leaves an entire class of skeptical hypotheses unscathed.
There are considerable difficulties in spelling out just what the real world hypothesis is, and I don’t take my version to be much beyond a bit of hand-waving. Vogel (1990) defines RWH as the body of our commonsense beliefs that account for the patterns and regularities exhibited by our sensory experience (p. 659). He explicitly excludes “advanced scientific beliefs” from RWH corpus. The reasons for this are (1) that it would be desirable for our knowledge of mundane facts about the world (e.g., that I have hands) not to depend on the frontiers of science, and (2) plausibly, people without advanced scientific knowledge should be able to know mundane facts about the world.
I’m sympathetic to these concerns, but a purely commonsense hypothesis will not do. Common sense is often wrong; common sense tells us that glass is a solid, for example, when it is, in fact, a slow-moving liquid. Another problem is that it is unclear what the real world hypothesis is—what is common sense to me might not be to you. If it is to pick out beliefs common to all, or some vast majority of people, then the real world hypothesis might be empty, or consist in just the vaguest, most general beliefs about the world. This sort of hypothesis would likely fail to contain anything like the spatial/geometric truths on which Vogel’s strategy relies (see Sect. 3).
BonJour (1999) provides a detailed account of what he calls the “quasi-commonsensical hypothesis”, which, like Vogel’s (1990) RWH, is supposed to map roughly on to common sense, without the need for advanced science. His full account is too long to detail here, but the central hypothesis is this:
[M]y sensory experiences are caused by a realm of 3-dimensional objects: (i) having at least approximately the shapes defined by what I have called the central sense-data, (ii) through which I move in such a way as to change my point of view, (iii) which are spatially related to each other in the ways reflected in the experiential sequences produced by my apparent movement, and (iv) which have causal properties and change over time in the ways corresponding to the relevant further aspects of experience (1999, 244).
One problem with BonJour’s account is that it must include at least some sophisticated scientific understanding of, e.g., the behavior of light and the laws of optics, otherwise it lacks a way to move from the existence of certain 3-d objects so arranged to the appearance of certain 3-d objects so arranged (much more on this below). Worries like these are why I specify a “scientifically informed” real world hypothesis. I think the idea is clear enough for the purposes here.
To “competently deduce Q from P” is, roughly, to start with P and correctly follow deductive rules of inference to arrive at Q.
Clark Glymour succinctly describes explanatory depth, as follows:
Ceteris Paribus, if T and Q are theories and for every established pair of regularities, H, K, such that Q explains H as a result of K, T also explains H as a result of K, but there exists established regularities, L, J, such that T explains J as a result of any other established regularity, T is preferable to Q. (1984, p. 184).
These characterizations follow Vogel’s (1990, p. 659).
Fumerton (2005) makes a point along these lines.
Or less simple. I avoid the ‘simpler’ locution because it is ambiguous between parsimony (having fewer ontological posits) and elegance (having fewer or more concise explanatory principles).
It is not clear to me that it is necessary that distinct physical objects do not overlap. Vogel (2005, p. 83, fn. 21) acknowledges such doubts, but does not concede the point. In this paper, I treat this as a necessary truth to accord with Vogel.
You may not share my intuitions that this sort of experience counts as an experience as of two distinct objects overlap**. It is hard to imagine what sort of experience would count. Perhaps it is impossible for us to have such an experience. If you think this, see my discussion of 3.11 below. If you think it is possible, but as a matter of contingent fact I have not had such an experience, then Sect. 3.3 will address this worry in detail.
Other examples in which Vogel is not explicit about this can be found in his (2005, p. 77) and (forthcoming). In these passages, Vogel seems to be more explicit. He is, but not about the right thing. He writes, for example:
If I walk two blocks north and then two blocks west, while you walk two blocks west and then two blocks north, we encounter the very same thing, whatever it may be, when we arrive. In the RWH, such facts are explained by [a] necessary truth… (2005, p. 77)
This passage is explicit about the mid-level facts being explained, not the experiential data at the top. That RWH explains this fact more elegantly than ISH is irrelevant. According to the ISH, we do not walk anywhere and encounter any thing (and, for that matter, there need be no we), so this is not something the ISH needs to explain at all.
Swap** ‘location’ for ‘apparent-location’ makes 3.10 equivalent to 3.11.
I am supposing the ‘extra-mental’ qualifier on the sorts of properties I am concerned with rules out properties like appearing red to Matt.
Of course, given that the laws of nature are deterministic, fixing the way the world is at any given point fixes the way the world is. Nonetheless, we can sensibly speak of other possible worlds having the same laws of nature as our world, but differing in some contingent matter of fact.
One skeptical hypothesis that I believe Vogel’s strategy successfully defeats is the hypothesis that I am dreaming. Dreams are almost characteristically disorderly—the impossible seems to happen at an alarming rate. So, the complete lack of such experiences seems to be strong evidence against the dreaming hypothesis. I do not, however, see any reason that this sort of disorderly appearance should be characteristic of, say, a computer simulation.
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Acknowledgments
Special thanks to Hilary Kornblith and Jonathan Vogel for their invaluable comments on earlier drafts.
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Gifford, M.B. Skepticism and elegance: problems for the abductivist reply to Cartesian skepticism. Philos Stud 164, 685–704 (2013). https://doi.org/10.1007/s11098-012-9879-6
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DOI: https://doi.org/10.1007/s11098-012-9879-6