Several of this blog’s frequent commenters find significant philosophical value in the concept of “common sense,” and find it helpful to refute a claim on the grounds that the claim contradicts “common sense.” These commenters include not only Thill, whom I challenged on the topic several times before, but Jabali108 and Neocarvaka. (See the comments on this post for examples.) So the concept is worth revisiting if those debates are to get anywhere.

Let me start out by noting that I see some philosophical value in appeals to common sense defined in a certain way. This is the sense that I outlined in my first post on the topic: the prejudgements one brings to a given inquiry, especially as they come out of shared assumptions of one’s own society. My commenters seem to have something quite different in mind, however. Thill said so explicitly in his first reply: he understands “common sense” not as socially shared assumptions or presuppositions, but as something else, something one might describe as more objective. His most recent (and probably clearest) statement on the subject contrasts common sense with “special training, e.g., items of scientific, technological, or aesthetic knowledge, scientific, technological, or aesthetic ways of knowing, and scientific, technological, or aesthetic standards of reasonableness,” and also with the paranormal or supernatural; but this ordinary or untrained sense, he claims, still provides us with reliable access to knowledge. (I discuss Thill’s exposition of “common sense” here because he has so far spelled it out more explicitly than the others.)

One must first note that the information that one learns without special training can be wrong. The point is clearest with respect to natural science, for the information one learns with scientific training so often contradicts the information one receives without it. I have returned repeatedly to a key example: untrained inference tell human beings that the sun goes up and comes down in the sky, in a manner similar to a baseball being launched and landing. This is a clear case in which “common sense” as Thill understands it is demonstrably wrong. Thill twice gave a wholly inadequate reply, based around the inarguable point that “Science does not deny that we perceive sunrise and sunset.” But that evades the important issue. The question I asked multiple times in response is: what is it that our supposed common sense tells us about the sun? Does it tell us merely that the sun is perceived to rise and fall (even though it actually doesn’t)? Then we can depend on common sense only to tell us about appearance and not about the truth of the matter; specialized training supersedes common sense when it comes to truth. Or does common sense tell us that the sun really does rise and fall? Then common sense is wrong in this case and can be wrong in other cases too, and we need specialized training to be able to tell when it is wrong and when it is right.

We made some progress in a discussion tangential to a more recent post. Here, as far as I can tell, Thill effectively admitted for the first time that common sense is fallible. It can be wrong; the fact that something is perceptible to the untrained, or widely understood among them, does not automatically make it correct.

This position appears to be a (welcome) change from a previous definition of common sense, as “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…” Fortunately, Thill is no longer treating common sense as true by definition, as he did in that previous definition. For then it would have been a useless tautology for establishing the truth: if common sense is necessarily true, then it does us no good to say that something is true because it is common sense, for that is merely saying it is true because it is true. To establish that something was common sense, we would need to establish its truth first, or we would not really have established that it was in fact common sense.

Rather, Thill’s admission that common sense is fallible comes in the context of distinguishing the infallible from the reliable. He compares common sense to visual perception: our eyes are fallible, as through optical illusions or hallucinations. But despite the existence of illusions and hallucinations, we can generally rely on our the evidence of our eyes, and we will be right the vast majority of the time.

But what reasons do we have to believe that “common sense” is indeed reliable at all, let alone reliable to the degree that visual perception is reliable? The latter claim is a most extraordinary one – and one for which I have seen precious little evidence or argument proffered. If the world can be known so easily without training, one wonders why one would ever bother with any training at all – including scientific training, which Thill has explicitly included among the kinds of training not necessary for common sense.

Science proves “common sense” wrong in a great many ways; sunrise and sunset are only the most obvious. Common sense tells us that a piece of rock is a continuous, solid whole; science tells us that in fact it is made of separate atoms that do not touch each other but are kept apart by force. Common sense even tells us that something as perfectly suited for its work as the human hand or eye could not have happened merely by random chance: the only non-biological phenomena we see with that degree of adaptation are the products of deliberate intentional design, by humans or other animals (such as a beaver dam or beehive). One can see this point without any specialized training; and when one does so, one is wrong.

But such situations, of course, are exactly what one should expect. People who think and train hard to learn about a given matter for a long period of time learn things about that matter that untrained people do not. It should come as no surprise that scientists know the workings of the natural world better than those with no scientific training, for they have worked long and hard at establishing conclusions that are better than everyday ones. To say that they do not is the lowest form of know-nothing populism. And similarly, though their methods are often different from scientists and though they are often wrong themselves, the views of the great philosophers are nevertheless usually more adequate and more profound than those of untrained “common sense.” Thinking about something longer usually makes you understand it better; if anything should be obvious to the untrained, it’s that point.

I have argued before that this is the great problem with relying too heavily on “intuitions” in ethics as well: there should be no primacy given to untrained knowledge. The whole point of training in something is to do better at it than do the untrained. There is no reason why the burden of proof should be on the trained. Rather, it should be on those who go against common sense in the first sense: the existing assumptions and prejudgements with which a debate implicitly begins.

I fully expect to get debate on the points above; but let me offer one caveat before it begins. You will be wasting your time if you try to refute anything I have said here with a comment like the first one here: “It is a non-sequitur to conclude that something must be good or great on the basis that a few or many have been reading or subscribing to it for a significant number of years. Just take a look at the history of superstition, religion, theology, ethics, and philosophy!” That history is exactly what I have been looking at in considerable depth for many years myself, and it is exactly that study that has convinced me the great thinkers of the past are much smarter than you or me, however many points they might be wrong about. I have little patience for that sort of question begging.