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Thill replies to my post about common sense in a reasonable way: by challenging the definition. In that post I have identified common sense as consisting merely of the prejudices common to any given age. Thill is right to protest that unmodified common sense, thus defined, will likely have few defenders (with the possible exception of Robert Goodin); and I did relatively little to defend my definition in that post. So it’s worth examining Thill’s alternative definition.

According to Thill’s quote, common sense is better defined in terms of:

the stock of Truths pertaining to the world naturally accessible to normal human beings anywhere on this planet and the faculties of the ordinary human mind employed in gaining access to those truths, e.g., that there is a world independent of our thoughts and desires, that there are other human beings, animals, and trees, the observable regularities of nature, human nature, and animal nature, basic uniform facts of human biology, etc.

Thill’s definition runs the risk of conflating two very different kinds of knowledge: those available to most human beings in the everyday course of their experience, and those which build on an accumulated body of knowledge derived from long, rigorous and systematic testing of hypotheses. The former can reasonably be called common sense. The latter – which of course is close to what we might normally call “science” – cannot.

It is a gross exaggeration to call the truths of science “naturally accessible.” Given the weight of scientific evidence that has accumulated over the past 200 years (or more), and the cost of equipment for scientific research, it is no longer possible even in principle for anyone to learn all the truths of science. They must instead be accepted on faith, on trust in scientific authorities. (I have previously claimed that this faith is not different in kind from faith in the Buddha or the Bible, but such a claim is not essential to the point at hand here; let us assume for the sake of the present argument that there is some sort of significant difference in kind between the two.) Long and sustained observation has told most human beings that the sun goes up and comes down in the sky, in a manner similar to a baseball being launched and landing. The claim that the sun does this is of course completely wrong; but it is naturally accessible to every human being with eyesight, it is what empirical observation tells the vast majority of us, to the point that we still speak of the sun “rising” and “setting” even when we know very well that the earth revolves around the sun and not vice versa. If one says “it is true that the earth is round and the sun revolves around it,” one is entirely correct and justified. If one says “it is common sense that the earth is round and the sun revolves around it,” one is either using “common sense” in the relativist sense that I advanced in the previous post – according to which “common sense” just means “the presuppositions of our society” – or one is being willfully blind.

But if we set aside the accumulated wisdom of modern natural science thus, Thill has still made a good point that there is a large body of knowledge available to human beings everywhere in their daily experience. One can cite many examples: that rocks fall when dropped, that human beings die when stabbed with a knife, that wet wood produces more smoke than dry wood, and so on. (I am particularly fond of the last example; thanks to it, reading Sanskrit philosophy made me better at barbecuing.)

This body of knowledge is real, and important. How shall we think about it? To my mind the most helpful way to classify it comes from the underrated anthropologist Robin Horton, in the concluding essay of his Patterns of Thought in Africa and the West. Horton began with a division between “commonsense” and “theoretical” thought, which he refined (respectively) into “primary” and “secondary theory.” Even with his anthropologically informed understanding, Horton notes that “primary theory really does not differ very much from community to community or from culture to culture.” (321) The entities it describes are the basic inhabitants of everyday experience: “people, animals, sticks, stones, rocks, rivers and so on.” (11) It does not speak of what these things are at a more level invisible to the naked eye (atoms, cells, illusions, ideas in the mind of God); rather, it describes relatively simple spatial, temporal and causal relationships among them. When we speak of things hidden to the naked eye, such as particles and waves or gods and spirits, then we have moved to the level of secondary theory, which is vastly alien from culture to culture. (Horton notes that his Nigerian undergraduates are as incredulous that anyone could disbelieve in spirits as New York undergraduates might be that anyone could believe in them.)

Horton moved from “common sense” to “primary theory” because he wanted to stress the commonalities between primary and secondary theory; but even to him, “common sense” had long seemed adequate as a way of speaking of primary theory. I don’t have a significant problem with using “common sense” to mean “primary theory,” in Horton’s sense; this is quite a different usage of “common sense” from the previous one, but quite defensible. The next question is: what then is the significance of this common sense for philosophical reflection? I will take up that topic next time.