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Last time, I accepted that there were two reasonable ways to define “common sense.” One can identify it with prejudices, as I did the first time around, so that common sense is what is held to be common and taken for granted by a given group of people (usually one’s own). Alternately, one can identify common sense with Robin Horton’s “primary theory”: the kind of description or explanation of human experience that is basic enough to be mostly universal, such as plants requiring water to grow. Primary theory is opposed to more complex “secondary theory” like witchcraft or subatomic physics, referring to unseen phenomena, which explains events anomalous to primary theory and is not at all universal.

Now if common sense is defined as primary theory, what then is its philosophical significance? Far less, I would argue, than is often claimed for “common sense.” The problems with primary theory are twofold: first, it is relatively limited in scope; and second, it is often wrong. Both of these problems can already be seen from the demarcation I laid out in the previous post – the point that common sense (thus defined) does not include the hard-won conclusions of natural science. Common sense can tell us that people who eat raspberries will be healthy and those who eat mistletoe berries will sicken; it doesn’t tell us why this is the case. That requires an accumulation of specialized knowledge gained through more systematic investigation. Similarly, common sense tells us that the sun goes up and goes down, as does a baseball – moving in the sky around a fixed earth – when in fact this is not the case at all, we are the ones who are moving.

Likewise, contra Thill’s comment, common sense does nothing to prevent racism, and historically has done much to support it. Thill claims “Common sense tells us that all humans have the same biology, i.e., a Jew is subject to the same biological processes an ‘Aryan’ or an Arab is subject to.” But to the extent that primary theory tells us this, it tells us the same about other primates, which are killed and nourished by more or less the same things that humans are. Humans outside our in-group, by contrast, can look just as alien as chimpanzees do, with their unintelligible languages and their strange tools or dress. And so indeed many tribes call themselves by a name that translates as “the people” – the common sense of everyday experience has told them that others were something not quite human. A more advanced secondary theory, a departure from common sense, was required to teach people the truth that we share a common humanity.

And so it is no strike against a philosophy that it denies common sense, in either sense of the term. I explained before why our understanding should be able to depart from prevalent ordinary beliefs. But if we aim at truth, we should also be ready to depart from primary theory. It is far removed from common sense to say that the earth revolves around the sun, or that apparently solid pieces of matter are mere collections of atoms; yet these claims are nevertheless true. And, to take us back to earlier discussions, the same can be said of Madhyamaka philosophies like Nāgārjuna’s that claim the world as we experience it is ultimately unreal. If one’s secondary theory did not at times and on some level contradict the primary theory, one could probably just stick with the primary theory and call it a day. But if one seeks genuine truth, one needs to do better than that.

Now it is reasonable to demand, as Aristotle does, that philosophy “save the appearances” to some extent: if one says that common sense – in either sense – is wrong, one must then go on to explain why it’s so common. One needs a theory of error. Some counterintuitive philosophies have a hard time providing this. Śaṅkara tries to tell us that truth is really one, indivisible; he grants that we perceive plurality, and argues that this perception is ignorance and error. But if everything is one and indivisible, how can there be ignorance? In order to be ignorance, wouldn’t it have to be a second thing, divisible from truth? One might argue Śaṅkara has ways of answering such an objection, but there’s no denying that it’s a thorny problem for him, comparable to the Abrahamic problem of suffering. If a philosophical system cannot adequately explain the existence and prevalence commonsense views (again, either in the sense of prevalent ordinary beliefs or the sense of primary theory), then that is a genuine strike against it. But the bare fact that it diverges from common sense is not in itself a problem.