But this is not the right question. The right question is, do you trust “the usual rules” more than you trust the output of your own brain (or, analogously, does Descartes trust “the usual rules” more than he trusts the output of his own brain)?
I certainly do! I have observed the fallibility of my own brain on numerous past occasions, and any temptation I might have had to consider myself a perfect reasoner has been well and truly quashed by those past observations. Indeed, the very project we call “rationality” is premised on the notion that our naive faculties are woefully inadequate; after all, one cannot have aspirations of “increasing” one’s rationality without believing that one’s initial starting point is one of imperfect rationality.
… Descartes may answer:
“Ah, but what is it that reasons thus? Is it not that very same fallible brain of yours? How sure are you that your vaunted rules are not, as you say, ‘imaginary distinctions’? Let us take away the rules, and see if you can build them up again. Or do you imagine that you can step outside yourself, and judge your own thoughts from without, as an impartial arbiter, free of all your biases and failings? None but the Almighty have such power!”
Indeed, I am fallible, and for this reason I cannot rule out the possibility that I have misapprehended the rules, and that my misapprehensions are perhaps fatal. However, regardless of however much my fallibility reduces my confidence in the rules, it inevitably reduces my confidence in my ability to perform without rules by an equal or greater amount; and this seems to me to be right, and good.
...Or, to put it another way: perhaps I am blind, and in my blindness I have fumbled my way to a set of (what seem to me to be) crutches. Should I then discard those crutches and attempt to make my way unassisted, on the grounds that I may be mistaken about whether they are, in fact, crutches? But surely I will do no better on my own, than I will by holding on to the crutches for the time being; for then at least the possibility exists that I am not mistaken, and the objects I hold are in fact crutches. Any argument that might lead me to make the opposite choice is quite wrongheaded indeed, in my view.
Now this is a curious example indeed! After all, if we take the “confidence in our grasp of geometry and logic” approach too far, then we will fail to discover that parallel lines are, in fact, sometimes not parallel. (Indeed, the oldest use case of geometry—the one that gave the discipline its name—is precisely an example of a scenario where the parallel postulate does not hold…)
And this is just the sort of thing we might discover if we make a habit of questioning what we think we know, even down to fundamental axioms.
It is perhaps worth noting that the sense in which “parallel lines are not parallel” which you cite is quite different from the sense in which our brains misinterpret the café wall illusion. And in light of this, it is perhaps also notable that the eventual development of non-Euclidean geometries was not spurred by this or similar optical illusions.
Which is to say: our understanding of things may be flawed or incomplete in certain ways. But we do not achieve a corrected understanding of those things by discarding our present tools wholesale (especially on such flimsy evidence as naive perception); we achieve a corrected understanding by poking and prodding at our current understanding, until such time as our efforts bear fruit.
(In the “crutch” analogy: perhaps there exists a better set of crutches, somewhere out there for us to find. This nonetheless does not imply that we ought discard our current crutches in anticipation of the better set; we will stand a far better chance of making our way to the better crutches, if we rely on the crutches we have in the meantime.)
Once again, you seem to be taking “the usual rules” as God-given, axiomatically immune to questioning, while Descartes… isn’t.
Certainly not; but fortunately this rather strong condition is not needed for me to distrust Descartes’ reasoning. What is needed is simply that I trust “the usual rules” more than I trust Descartes; and for further clarification on this point you need merely re-read what I wrote above about “crutches”.
Explicable to whom? To yourself, yes? But who or what is it that evaluates these explanations, and judges them to be persuasive, or not so? It’s your own brain, with all its failings… after all, surely you were not born knowing these rules you take to be so crucial? Surely you had to be convinced of their truth in the first place? On what did you rely to judge the rules (not having them to start with)?
The fact is that you can’t avoid using your own “naive, unconstrained” reasoning at some point. Either your mind is capable of telling right reasoning from wrong, or it is not; the recursion bottoms out somewhere. You can’t just defer to “the rules”. At the very least, that closes off the possibility that the rules might contain errors.
I believe my above arguments suffice to answer this objection.
[...] I certainly don’t think it’s obviously true that a program can’t determine whether it’s running or not.
Suppose a program is not, in fact, running. How do you propose that the program in question detect this state of affairs?
I do think that any received answer to such a question can only be “yes” (because in the “no” case, the question is never asked, and thus no answer can be received).
But why is this a problem, any more than it’s a problem that, e.g., the physical laws that govern our universe are necessarily such that they permit our existence (else we would not be here to inquire about them)? This seems like a fairly straightforward case of anthropic reasoning, and we are all familiar with that sort of thing, around here…
If the only possible validation of Descartes’ claim to exist is anthropic in nature, then this is tantamount to saying that his cogito is untenable. After all, “I think, therefore I am” is semantically quite different from “I assert that I am, and this assertion is anthropically valid because you will only hear me say it in worlds where it happens to be true.”
In fact, I suspect that Descartes would agree with me on this point, and complain that—to the extent you are reducing his claim to a mere instance of anthropic reasoning—you are immeasurably weakening it. To quote from an earlier comment of mine:
It seems to me that, on the one hand, that the program cannot possibly be wrong here. Perhaps the statement it has printed is meaningless, but that does not make it false; and conversely if the program’s output were to be interpreted as having meaning, then it seems obvious that the statement in question (“I exist”) is correct, since the program does in fact exist and was run.
But this latter interpretation feels very suspicious to me indeed, since it suggests that we have managed to create a “meaningful” statement with no truth-condition; by hypothesis there is no internal logic, no conditional structure, no checks that the program administers before outputting its claim to exist. This does not (intuitively) seem to me as though it captures the spirit of Descartes’ cogito; I suspect Descartes himself would be quite unsatisfied with the notion that such a program outputs the statement for the same reasons he does.
I certainly do! I have observed the fallibility of my own brain on numerous past occasions, and any temptation I might have had to consider myself a perfect reasoner has been well and truly quashed by those past observations. Indeed, the very project we call “rationality” is premised on the notion that our naive faculties are woefully inadequate; after all, one cannot have aspirations of “increasing” one’s rationality without believing that one’s initial starting point is one of imperfect rationality.
Indeed, I am fallible, and for this reason I cannot rule out the possibility that I have misapprehended the rules, and that my misapprehensions are perhaps fatal. However, regardless of however much my fallibility reduces my confidence in the rules, it inevitably reduces my confidence in my ability to perform without rules by an equal or greater amount; and this seems to me to be right, and good.
...Or, to put it another way: perhaps I am blind, and in my blindness I have fumbled my way to a set of (what seem to me to be) crutches. Should I then discard those crutches and attempt to make my way unassisted, on the grounds that I may be mistaken about whether they are, in fact, crutches? But surely I will do no better on my own, than I will by holding on to the crutches for the time being; for then at least the possibility exists that I am not mistaken, and the objects I hold are in fact crutches. Any argument that might lead me to make the opposite choice is quite wrongheaded indeed, in my view.
It is perhaps worth noting that the sense in which “parallel lines are not parallel” which you cite is quite different from the sense in which our brains misinterpret the café wall illusion. And in light of this, it is perhaps also notable that the eventual development of non-Euclidean geometries was not spurred by this or similar optical illusions.
Which is to say: our understanding of things may be flawed or incomplete in certain ways. But we do not achieve a corrected understanding of those things by discarding our present tools wholesale (especially on such flimsy evidence as naive perception); we achieve a corrected understanding by poking and prodding at our current understanding, until such time as our efforts bear fruit.
(In the “crutch” analogy: perhaps there exists a better set of crutches, somewhere out there for us to find. This nonetheless does not imply that we ought discard our current crutches in anticipation of the better set; we will stand a far better chance of making our way to the better crutches, if we rely on the crutches we have in the meantime.)
Certainly not; but fortunately this rather strong condition is not needed for me to distrust Descartes’ reasoning. What is needed is simply that I trust “the usual rules” more than I trust Descartes; and for further clarification on this point you need merely re-read what I wrote above about “crutches”.
I believe my above arguments suffice to answer this objection.
Suppose a program is not, in fact, running. How do you propose that the program in question detect this state of affairs?
If the only possible validation of Descartes’ claim to exist is anthropic in nature, then this is tantamount to saying that his cogito is untenable. After all, “I think, therefore I am” is semantically quite different from “I assert that I am, and this assertion is anthropically valid because you will only hear me say it in worlds where it happens to be true.”
In fact, I suspect that Descartes would agree with me on this point, and complain that—to the extent you are reducing his claim to a mere instance of anthropic reasoning—you are immeasurably weakening it. To quote from an earlier comment of mine: