Thursday, March 10, 2022

Common Sense as a Test of Theory

 Marcus Arvan has an article, Common sense leads philosophy astray, in which he argues that common sense should not be a standard philosophy is tested against. It fails, and it fails almost immediately, because Arvan's argument does not rely on any rigorous experimentation or technical logic but entirely on commonsense assumptions about how evidence and theory work. Reject common sense as a standard against which philosophical argument has to be measured and Arvan's argument against common sense as a standard against which philosophical argument has to be measured can't get off the ground.

This is actually not a minor or surprising point; Duhem makes a similar point about physical theories, which he argues always have to be tested against common sense. But what about the cases Arvan mentions in his third point:

Third, better methods—specifically, scientific methods—have a long track record of refuting commonsense beliefs that people once (falsely) took to be knowledge. For example, it was once taken for granted, as commonsense knowledge, that the Earth is flat and stationary—yet we now know from scientific inquiry that the Earth is spherical and revolves around the Sun. The history of science is full of examples like this. Darwin’s theory of evolution, Einstein’s theory of relativity, quantum mechanics, etc.—all refuted commonsense beliefs about the world that people thought to be knowledge.

There are many problems with this line of thought. Here are three in particular.

(1) What Arvan is doing in part is eliding 'belief' and 'commonsense belief' without properly distinguishing the two -- a 'commonsense belief' has to be something we can generally share in the interpretation of common experience, and when you try to press what 'commonsense belief' quantum mechanics is supposed to have refuted, for instance, it always turns out to be a very technical claim that requires Newtonian mechanics to state correctly. Even assuming that scientific theories occasionally refute commonsense beliefs, this is necessarily accidental; scientists are typically trying to refute scientific theories, and it's very common when they look at looser claims that they have to make extensive assumptions to operationalize the claim so that it's even something they can bring their experiments or observations to bear on. And all of the theories that Arvan mentions get results that some people consider counterintuitive by going to extremes outside of common experience -- extreme smallness, extreme swiftness, extreme lengths of time, vast expanses beyond what any one person can easily explore.

(2) While Arvan correctly elsewhere distinguishes commonsense belief and commonsense knowledge, he fails to take it with proper seriousness here. No one expects that commonsense belief would be infallible -- it's not commonsense knowledge. What Arvan needs to argue is that commonsense belief is not presumptively approximately right. That is, the claim of importance is not 'If something contradicts commonsense belief, it must be wrong' but claims like 'If something contradicts commonsense belief, it needs the support of an especially rigorous or evidence-heavy argument' or 'If something contradicts commonsense belief, one needs a well-supported error theory for how commonsense belief went wrong'. We don't have to take commonsense beliefs to be the criterion of truth in order to take them as something we need to test our arguments and claims against.

(3) But more seriously than all of these is the primary point that Duhem makes about common sense and science: all scientists test their theories against common sense. How might a scientist test something? By taking measurement. How do you take such a measurement? Well, you have a measuring device that you assume, on the basis of common sense recognition of the stability of things, is not going to suddenly act in a completely different way from usual without a cause, and you look at its output (in whatever form that might be) and you trust, on the basis of common sense recognition of the senses as evidence, that your senses are giving you something at least approximately accurate assuming that there is no interfering cause, and  you record the measurement on the commonsense assumption that your recording device (whether memory, paper, or anything else) will accurately retain what you are recording on it as long as nothing makes it not do so, and you examine your measurements and you ask, "Do these measurements make sense?" on the basis partly of prior scientific theories and partly of common sense about what kind of answers you could be getting with that kind of measurement, and then if they don't make sense, you might check for all those interfering causes by using commonsense assumptions about how causes can interfere with measurements, and then (since measurements generally cluster rather than exactly hit every time), you draw your conclusions about how these measurements should be interpreted as measurements, which you don't always do by rigorous logical argument within a formal system but often by commonsense principles of argument.  You can talk about the theory of relativity refuting common sense all you want, and it is still the case that all of the evidence for it can only be gathered by relying on common sense, and if someone proposes alternative possibilities for how to gather and interpret the evidence, one of the ways you determine whether they are a crackpot or not is whether their proposal even meets the basic standards of common sense. If someone claims that all the evidence for relativity is forged in undiscoverable ways by an evil deceiver, physicists are going to dismiss this, not on the basis of physical theory, but on the basis of common sense.

Arvan has a number of arguments, of course; some of them are simply wrong. (Filmer's religious opinions were not 'commonsense religious beliefs' but extremely controversial and often not widely shared even among Christians, much less human beings generally.) I think the best of them is this one:

Second, appeals to commonsense in philosophy are a demonstrably unreliable method for distinguishing genuine knowledge (and truth) from mere belief (and falsehood). How do I know this? As Jason Brennan points out, philosophers disagree wildly over philosophical issues. Take any philosophical debate you like—consciousness, free will, morality, epistemology, justice, etc.—you will find a wide plurality of mutually incompatible arguments and theories. Because mutually incompatible claims cannot be true, it follows that virtually all philosophical arguments and theories are unsound, having false conclusions.

This is for the most part true enough, but to regard it as relevant here seems to be relying on a number of assumptions that are dubious at best, and, I think, certainly false: for instance, that almost all of these philosophical theories are well-supported by common sense itself, for instance, or that almost all of the disagreements among philosophers are completely within the field of things that can be adjudicated by appeal to common sense alone. It is true that, just as physicists all assume common sense when they are taking readings, philosophers all assume common sense sometimes. But they all use evidence and logic sometimes, too, and that on its own doesn't do anything about philosophical disagreement. Philosophers often miss evidence, and they often miss logical steps or are arguing with loose, nonrigorous arguments, and they often fail to consider various facets of common sense about our common experience, and they often talk about things that are difficult in that it takes a lot to work through all the ramifications of all of these things, and all of this suffices to explain divergences even if philosophers use common sense, evidence, and logic.

Common sense is definitely a test of theory; biologists, chemists, physicists, and mathematicians have to rely on it as a test as much as, perhaps more than, philosophers. It is not a criterion of truth, and commonsense beliefs can be proven wrong, as Arvan says, although he grossly exaggerates how often they are. (One can in fact argue that common sense is extremely good on the basis of how rarely it is proven completely wrong, how it virtually always takes our very most brilliant science to do it, and how limited the resulting refutations are.) They also don't have unlimited scope; lots of fields eventually reach a point that is well outside the kind of common experience that common sense interprets, although they all do so from a platform within common experience. But these limitations don't in any way reduce the value of common sense as a test, even if under 'common sense' we include a lot of the gray areas. If a position seems to violate common sense, that needs explanation and the position needs to be supported by arguments for why it should be regarded as true despite the apparent violation of common sense. And this is not surprising. Common sense is evidence, namely, what non-crazy people find most useful in attempting to navigate common experience, and apparently violating it is apparent inconsistency with some of the evidence.