Rae Langton (“Elusive Knowledge of Things in Themselves,” Australasian Journal, 2004) and Jonathan Schaffer (“Quiddistic Knolwledge,” Phil. Studies, 2005) have recently argued that the ‘skeptical’ thesis defended by David Lewis in “Ramseyan Humility” is no different, when it comes to the applicability of standard anti-skeptical proposals, from Cartesian skepticism. It seems to me, though, that Lewis – at least on a charitable reading – could not have meant what Langton and Schaffer take him to mean.
On the face of it, of course, Lewis’ humility thesis (“We have no knowledge of the instrinsic properties of things”) looks like the same kind of claim as Cartesian skepticism (“We have no knowledge of the external world”). And Langton and Schaffer stress the similarities in the arguments that Lewis and the Cartesian offer – both arguments appeal to the idea that there are a plurality of possibilities which are all equally supported by our evidence. In the Cartesian case, this evidence is (among other things) our perceptual experience, which supports (so the Cartesian argues) the hypothesis that there is an external world just as much as it supports the hypothesis that we are decieved by an evil demon. In the case of Lewis, the evidence is our scientific evidence – what we know (or have sufficient reason to believe) about the world is that a certain Ramsified sentence (encompassing both our ordinary beliefs about the world, along with our best scientific theories) is true. And this evidence, so Lewis argues, supports the hypothesis that the fundamental, instrinsic properties of things are p1, p2, p3, etc. just as much as it supports the hypothesis that the fundamental, instrinctic properties of things are q1, q2, q3, etc. There are “multiple realizations” (as Langton puts it) of the Ramsified sentence, since we can imagine different permutations of fundamental, instrinsic properties underlying the same causal superstructure, i.e. (and more importantly) warranting the same belief in the same Ramsified sentence. And knowledge that that sentence is true exhausts our (scientific and ordinary) knowledge.
So we have no knowledge of the fundamental, instrinsic properties of things.
But wait a minute. In Descartes’ argument, it is claimed that although I believe one thing (that there is an external world), my evidence actually equally supports another incompatible thing (that I’m decieved). But that is not claimed in Lewis’ argument. It is not that I believe that the fundamental, instrinsic properties of things are p1, p2, p3, etc., and then Lewis points out that my evidence equally supports the hypothesis that the fundamental, instrinctic properties of things are q1, q2, q3, etc. What I believe is that the Ramsified sentence, described above, is true. And that not only exhausts my knowledge, it exhausts my belief. The Cartesian skeptic argues that we are overly credulous – believing in an external world, without sufficient warrant. But Lewis does not argue that we are overly credulous.
Consider the beliefs that I do have about the fundamental properties of things. I believe, for example, that some particles have charge, and I think that charge obeys Coulomb’s Law. But Lewis’ argument does not challenge these beliefs. If that were what Lewis was saying – that I do not know that charge obeys Coulomb’s Law, because for all I know it is spin that obeys Coulomb’s Law, and not charge – that would make his argument akin to Descartes’ argument. And I think it would be right to reject it, on whatever grounds we reject Descartses argument. But it doesn’t seem to me that that could be what Lewis was saying.
He writes, on p. 16-17 of my manuscript, that our ignorance of instinsic properties is ineffable, because we would like to express our ignorance by listing (by name) the possible properties which fulfill a certain causal role (described by the Ramsified sentence), but we can’t. We do not have names for these properties. The property-names that we do have – ‘charge’, ‘spin’, ‘mass’, etc. – are not the names we want. The problem of our ignorance is not, on Lewis’ view, the problem of knowing whether any bodies have charge, the problem is knowing what property ‘charge’ picks out. (Or, if you prefer, the problem is knowing what property it is that in virtue of having it, things have charge.) Consider an analogous case: we have no knowledge of who the murderer is. This is because, let us suppose, that although we have evidence enough to suppose that there is some person who fulfills the role of ‘the murderer’, we do not know who the murderer is. But this ignorance is not Cartesian ignorance – it is not as we believe that the murderer is Jones, but do not have sufficient warrant for this belief. The point here is just that ignorance need not mean unjustified belief – ignorance is sometimes a lack of belief. In the case of the ignorance of fundamental, instrinsic properties defended by Lewis, it seems to me that it is the latter kind of ignorance. (Furthermore, it seems that what Lewis’ argument shows, if it is correct, is that we couldn’t form the beliefs in question – we don’t have the ability to express those propositional contents, the ones of which Lewis says that we can’t know whether they’re true or not. But this means that our ignorance is to our epistmeic benefit! Our inability to so much as believe one of Lewis’ true, unknowable propositions ensurses that we won’t form any unjustified beliefs, when it comes to fundamental, instrinsic properties.)
This, it seems to me, is why the situation is not “ominous” – because Lewis has not uncovered a domain of belief where we have rashly gone beyond our evidence (as the Cartesian claims). The thesis that most of my beliefs are unjustified, and the possibility that most of them are false, is ominous. But the thesis that there are some things (about the fundamental nature of things) I won’t ever be able to know – that’s not ominous at all.
A caveat: I find Lewis’ essay quite confusing, and I certainly wouldn’t be that surprised if I was wrong about what he meant. But if he really did mean that I don’t know that charge obeys Coulomb’s Law, because it’s possible that spin obeys Coulomb’s Law – well, that seems to me to be a somewhat bad argument, and it really doesn’t seem to have anything to do with the fact that charge is a fundamental property, or with the nature of intrinsic properties, or whatever. On the reading I’ve offered, we at least get the result that Lewis’ argument really does offer us something new – not just Cartesian skepticism “writ small” (as Schaffer argues) – and something that really is a consequence of the nature of fundamental, instrinsic properties.