On a question of Mohan Matthen
Mohan Matthen writes at NewAPPS:
p: I am sitting here writing a blog post. It is now later than when I wrote the previous sentence.
Can I doubt the truth of what I just wrote?
Let’s say I can rationally doubt p if there is some scenario S that falsifies p, and I cannot conclusively rule S false. Certainly there are admissible scenarios that falsify p: I may be dreaming. So I can rationally doubt p.
Let’s say doubt is sceptical if it spreads to unrelated propositions. The dream scenario falsifies p, but it also falsifies everything else I seem to perceive. Let’s say a doubt is empirical if it does not spread. I may doubt that my computer is working properly. But this doubt, based on the computer’s odd performance, does not spread to the proposition that my printer is working properly. (More details here.)
I would claim that I cannot empirically doubt p. I can doubt that it is now later than when I started writing, but only by dream scenarios and other sceptical stratagems that cast doubt on all contingent propositions.
p: I am writing a blog post. My fingers are above the keyboard. Can p be doubted?
In a way, no. But an Aristotelian would hold that up and down are absolute notions: ‘up’ is away from the center of the universe, ‘down’ is toward it.
The Newtonian says: no, ‘up’ is the direction toward the center of some nearby large mass, and ‘down’ is away from that center; ‘up’ and ‘down’ are notions of purely local application (and in some reference frames, simply inapplicable); the Aristotelians’ ‘up’ and ‘down’ is “overturned” as being, though conceivable, of no application anywhere.
As for ‘above’, “x is above y” will mean that y and x lie along a line incident with the center of the nearby mass that defines ‘up’ and ‘down’, and that y is farther from that center. So understood the relation ‘is above’ (new style) is coextensive with the relation ‘is above’ (old style). Moreover, various commonplaces about aboveness can be explained in the new system, e.g. that it takes effort to situate one thing above another, or that if y is above x then y, if left unsupported, will fall on x.
Can the Newtonian be said to doubt that her fingers are above the keyboard? Notice that in the exchange above, statements (or, for that matter, thoughts) in which the relation of aboveness figures have been given two interpretations. I want to emphasize both two and interpretation. The original thought—that my fingers are above the keyboard—is not interpreted, and not itself an interpretation of something else. It’s just there, as something I think or say (you could add: on the basis of certain experiences, but that doesn’t seem to advance the argument).
The two interpretations seem to be incompatible, or rather they seem to have incompatible consequences in a world in which there is more than one candidate for “nearby large mass”.
The Aristotelian is committed to holding that if I am sitting on the visible side of the moon with my head pointing toward the Earth, my feet are above my head (‘above’ being understood Aristotelian-wise); the Newtonian is committed to holding that my head is above my feet (‘above’ being understood Newtonian-wise); and commonsense says that if x is (properly) above y, then y is not properly above x. (I have to bring in commonsense here, because there is no incompatibility between what the Aristotelian says and what the Newtonian says except through mediation by the “naïve” notion of ‘above’.)
My attitude toward my naïve belief that my fingers are above the keyboard cannot accurately be characterized as “doubt”. As a convert to Newtonianism, I am no more inclined to doubt that claim empirically than I was before I was converted (and whether I was converted from naïveté or from Aristotelianism). Newtonianism, like Aristotelianism, gives me an interpretation under which the claim is true.
On the other hand, I do, after a fashion, rationally doubt the claim insofar as I can imagine a scenario in which it, but also every other statement of a certain type, turns out false (e.g. if there were an even larger mass than Earth nearby and in the feet-to-head direction). Indeed, Newtonian physics gives me a systematic reason to relinquish the naïve notion of aboveness altogether insofar as it, along with various other notions about bodies and space, has a fatal connection with Aristotelianism (as many 17th-century philosophers thought it did). (The “retraining of intuitions” that Eric refers to was in part a relinquishment of Aristotelian/commonsense notions, e.g. of nonrelative rest and of differences between qualitative and specific change—alteration as contrasted with corruption. Descartes is quite explicit about this in Le Monde. Boyle in his Origin of forms and qualities devotes quite a bit of effort to convincing his reader that there is no distinction to be made between alteration, or change of quality, and generation and corruption, or change in substantial form; some of that effort consists in persuading his reader to give up Aristotelian interpretations of common experiences.)
I’m not sure whether commonsense notions of ‘before’ and ‘after’ stand to General Relativity as do commonsense notions of ‘above’ and ‘below’ to Newtonian (and post-Newtonian) physics. I suspect that in the world imagined by George Gamow, in which the speed of light is about 20 miles an hour, ‘before’ and ‘after’ would prove less useful, because simultaneity relations are not relativistically invariant. That would not lead me, exactly, to doubt that it is now later than when I wrote the previous sentence; but, as before, it would lead me to reinterpret what I take myself to mean when I make statements like that, and perhaps, in time, to relinquish ‘before’ and ‘after’. I would, for example, introduce the concept of worldline in interpreting commonsense notions of ‘before’ and ‘after’; and I would learn that those notions are applicable only along worldlines.