Paradox: The incoherence of common sense

My musings on mathematicians and engineers were provoked by my Love’s reaction to something I saw in a quotes file:

There’s no way to develop an ambitious, broad-ranging, self-consistent metaphysical system without doing serious violence to common sense somewhere.
Eric Schwitzgebel

When I saw that, I laughed. It sums up what I’ve always thought about metaphysics. It sums up what almost everyone thinks about analytic philosophy.

I quoted it to my Love, who was trained as a pure mathematician. (For those of you who have never spent time with a pure mathematician: They make Mr Spock seem illogical.) She smiled and said,

Of course, sweetheart. Everything in mathematics, everything in science, did serious violence to the common sense of its time. That’s why we remember Galileo and Newton and Euler and Einstein. They defied common sense. Common sense is always wrong, unless it’s based on science that did violence to the common sense of its time.


The perils of quotes files: They lack context.

After that conversation with my Love, I read the whole interview with Professor Schwitzgebel. He said essentially the same thing as my Love said. He’s not criticizing metaphysics. He’s criticizing common sense. I still think metaphysics (other than Kant) is mostly silly, but he’s devastatingly right about common sense.

In context, Professor Schwitzgebel says,

Common sense is incoherent in matters of metaphysics. There’s no way to develop an ambitious, broad-ranging, self-consistent metaphysical system without doing serious violence to common sense somewhere. It’s just impossible. Since common sense is an inconsistent system, you can’t respect it all. Every metaphysician will have to violate it somewhere.

Common sense is an acceptable guide to everyday practical interactions with the world. But there’s no reason to think it would be a good guide to the fundamental structure of the universe. Think about all the weirdness of quantum mechanics, all the weirdness of relativity theory. The more we learn about such things, the more it seems we’re forced to leave common sense behind. The same is probably true about metaphysics.

You don’t even need to get into the weirdness of quantum mechanics. The Sun orbits the Earth? Common sense. A heavier stone falls faster than a lighter stone? Common sense. Species were as God created them in the Garden of Eden? Common sense. Newtonian mechanics? Crazy. Invisible animals cause disease? Insane! Send pictures through the air? Get this guy a straitjacket.


Even in the most abstract pursuits, there’s a place for common sense. Professor Schwitzgebel again:

But here’s the catch: Without common sense as a guide, metaphysics is hobbled as an enterprise. You can’t do an empirical study, for example, to determine whether there really is a material world out there or whether everything is instead just ideas in our minds coordinated by god. You can’t do an empirical study to determine whether there really exist an infinite number of universes with different laws of physics, entirely out of causal contact with our own. We’re stuck with common sense, plausibility arguments, and theoretical elegance – and none of these should rightly be regarded as decisive on such matters, whenever there are several very different and yet attractive contender positions, as there always are.

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