Wittgenstein on the Inverted Spectrum

The Stanford Encyclopedia of Philosophy entry on "Inverted Qualia" begins by noting that "Qualia inversion thought experiments are ubiquitous in contemporary philosophy of mind (largely due to the influence of Shoemaker 1982 and Block 1990). The most popular kind is one or another variant of Locke's hypothetical case of “spectrum inversion”, in which strawberries and ripe tomatoes produce visual experiences of the sort that are actually produced by grass and cucumbers, grass and cucumbers produce experiences of the sort that are actually produced by strawberries and ripe tomatoes, and so on." This paper reviews and evaluates what Wittgenstein had to say on the topic. In the Philosophical Investigations , Wittgenstein observes that the idea of private experience, "that nobody knows whether other people also have this or something else" (sec 272) supports the assumption that it is possible, but unverifiable, that "one part of mankind had one sensation of red, and one part another", and thus the possibility of spectrum inversion. However, he does not explicitly discuss such hypotheses. Recently, Block (2007) has drawn attention to Wittgenstein's discussion of spectrum inversion in the "Notes for Lectures on 'Sense Data.'" There, Wittgenstein discusses "cases in which we should say that the person sees green what I see red" (Wittgenstein 1993, 285), conceding that a single person case of spectrum inversion is conceivable, but denying that this could always be the case. Block argues that a slippery slope leads from the concession of the possibility of spectrum inversion in a particular case to a scenario in which many people experience long-term spectrum inversion, and that such scenarios are verifiable hypotheses. I evaluate Block's critique of Wittgenstein, and Canfield's (2009) response to Block's reading.