Culture

Species of speciousness 5: conceivability and possibility

September 05, 2007
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If we can think it, does that make it possible, or even true? Descartes argued something like this in part four of his seminal Discourse on the Method of Rightly Conducting the Reason, and Seeking Truth in the Sciences. Having laid the foundations of modern philosophy with the declaration that his own thinking was a matter of certainty in an otherwise radically uncertain world, he went on to argue that, since he had within his thinking an idea of perfection, there must be such a thing as a perfect being who gave him this idea—

…for to receive it [i.e. the idea of perfection] from nothing was a thing manifestly impossible; and, because it is not less repugnant that the more perfect should be an effect of, and dependence on the less perfect, than that something should proceed from nothing, it was equally impossible that I could hold it from myself: accordingly, it but remained that it had been placed in me by a nature which was in reality more perfect than mine, and which even possessed within itself all the perfections of which I could form any idea; that is to say, in a single word, which was God.
The problem with thought experiments, of course, is that we tend to rig them. Descartes, if pushed, could probably have imagined a perfect chess player or a perfect baker, or even a perfect loaf of bread. Does that mean that he had met such people, or that such things necessarily exist? Only if you believe that conceptions have a necessary relationship with actuality, a position not many modern philosophers would maintain.

Gods and perfection may be out of fashion, but thought experiments remain useful and frequently deployed—and dangerous. On which topic, I have finally got around to reading Nassim Nicholas Taleb's The Black Swan (as reviewed by Mr Tom Nuttall for Prospect) and found it engaging but overly populated by "experiments" that offer vividness but little in terms of argument.

Near the start, for instance, Taleb asks us to consider "the following thought experiment": the hypothetical possibility of a legislator who on the 10th September 2001 enacted a measure that "would certainly have prevented 9/11." So in Taleb's parallel world, this particular atrocity never happened—no planes were hijacked, no mass-murder was conducted. This, Taleb goes on, is a demonstration of our species's fundamental misguidedness—because the legislator who saved these lives is not treated as a hero, or even remembered for his actions. "We humans," he concludes, "are not just a superficial race… we are a very unfair one."

There's a striking point being made here, but it can hardly be said to be a "thought experiment." Taleb's parallel world exists only to illustrate his point. How does he know his legislator wasn't rewarded? How does he know disaster was averted so seamlessly that it might as well have never been? Because he made the story up. It's an illustration, but not an argument; and it's doubly suspect because it relies upon the one thing his entire book assures us is impossible—complete predictability. Only in our minds can we say that one thing will "certainly" lead to another: the real world does not work like this, and it is fallacious to say that it does even in retrospect or hypothesis. Doubt, as Descartes knew, is the only guarantee we have. Gods and certain connections may be comforting, but their conceivability does not make them real.