Bryan Caplan  

The Quantum Leap of Logic

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Quantum mechanics is often used as a club against common sense.  I've heard dozens of variations on Scott's:
After all, quantum mechanics doesn't sound plausible either---but it's true.
Seriously, though, how does this argument amount to anything more than:
Common sense is an unreliable guide to claims completely outside of ordinary experience.  Therefore, common sense is an unreliable guide to claims well within ordinary experience.
As Merlin says in Excalibur, "You'll have to do better than that."

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COMMENTS (14 to date)
Rocinante writes:

Sounds like you're carving out lifeboat exceptions to epistemology.

Paul Ralley writes:

Common sense tells you that your world is flat, the sun rises, and protectionism protects.

Nick writes:

I am not sure whether "efficient markets, rational expectations, the supply-side effects of high MTRs" qualify as "within ordinary experience" during the 500,000 years or so that common sense evolved. That is Scott's entire point, namely, that common sense does not provide explanations for complex systems that have only existed for a short time relative to the human brain's ability to evolve to deal with them. However, our (semi-)scientific system of observation and experimentation (the field of economics) is appropriate to understand and explain these systems.

Lee Kelly writes:

Sure, common sense is instrumentally effective in a large range of everyday circumstances. If it wasn't, then it wouldn't last. I don't believe Scott is suggesting otherwise. The point is just that common sense also fails in many important circumstances, especially in matters of social policy.

Les Cargill writes:

What it means is that common sense is fine - as far as it goes. Once you begin to use a rigorous system of measurement and reasoning about something, you're no longer bound by common sense.

What that has to do with macroeconomics, I don't know.

Greg G writes:

The weirdness and reliability of quantum physics are easily and often misused in trying to justify other ideas that are weird but unreliable.

But in this case, I have to side with Scott. Common sense sometimes fails in ordinary experience. It is a perfectly ordinary experience to stand still on the earth and feel you really are still even though you are standing on a big round rock spinning at 1,000 miles an hour.

The Newtonian idea that everything is moving all the time referred to common experience but was not derived from common sense. It was based on impeccable logic but I'm pretty sure no one will want to claim that impeccable logic is "common."

Common sense is just a useful heuristic. I don't see Scott saying it is usually "unreliable" in ordinary experience - just that it is sometimes unreliable in ordinary experience.

RPLong writes:

I had the opposite criticism: What on Earth sounds implausible about quantum mechanics?

The only lesson worth drawing from this is that people come to different conclusions when they know something about the subject matter than they do when they know nothing about it at all. That's no big revelation, and certainly not at odds with anything Sumner was writing about.

Tom West writes:

I suspect that what Bryan considers common sense is pretty darn uncommon. Or, to paraphrase, "I don't think those words mean what you think they mean."

I like Bryan's sense of common sense (even if it doesn't match my own), but I think it's helpful for those who are cognitively different to pay close attention to how other people use phrases like this.

Jameson writes:

RPLong, have you even heard of the double-slit experiment? Anyone who claims that the result of this experiment is plausible to their common sense is just being disingenuous.

I have mixed feelings about Caplan's critique, here. On the one hand, sure, common sense is both a necessary and good starting point for trying to solve life's mysteries. On the other hand, modern writers often need a quick way to convince their audience not to recoil from a conclusion that seems to violate common sense. The quantum mechanics example works because, unlike economics, no one has a vested ideological interest in it.

Yet I'm not sure the comparison is very effective. To convince people of the strange claims of quantum mechanics, you just show them the experiment. They won't believe their eyes at first, so just repeat the experiment until they're convinced. That there could be such a repeatable, controlled experiment in macroeconomics is, on its face, rather preposterous.

Greg G writes:

Tom West,

You might well be right but, if you are, Bryan would be able to communicate more effectively if he stopped calling it that.

RPLong writes:

@ Jameson - Your Wikipedia link lists no less than four possible interpretations of the experiment. Which of those do you find counter-intuitive?

Greg G writes:


The point isn't that the explanations are necessarily counterintuitive once you know about the phenomenon.

The point is that the existence of the phenomenon itself was extraordinarily counterintuitive. That is why the effect wasn't easier to predict and still surprises many people when they see it.

RPLong writes:

Greg G - Agreed. You and I are saying the same thing: "people come to different conclusions when they know something about the subject matter than they do when they know nothing about it at all." I only add that this phenomenon should neither count in favor of common sense nor against it.

ThomasH writes:

But the tricky think about applying common sense to common sense to know when claims well within ordinary experience is knowing when they ARE within ordinary experience. Bastiat is common sense at full employment but not at less then full employment.

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