Prior Probabilities

Common Sense

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I have tended to emphasize common sense as a basic source in attempting to philosophize or otherwise understand reality. Let me explain what I mean by the idea of common sense.

The basic idea is that something is common sense when everyone agrees that something is true. If we start with this vague account, something will be more definitively common sense to the degree that it is truer that everyone agrees, and likewise to the degree that it is truer that everyone agrees.

If we consider anything that one might think of as a philosophical view, we will find at least a few people who disagree, at least verbally, with the claim. But we may be able to find some that virtually everyone agrees with. These pertain more to common sense than things that fewer people agree with. Likewise, if we consider everyday claims rather than philosophical ones, we will probably be able to find things that everyone agrees with apart from some very localized contexts. These pertain even more to common sense. Likewise, if everyone has always agreed with something both in the past and present, that pertains more to common sense than something that everyone agrees with in the present, but where some have disagreed in the past.

It will be truer that everyone agrees in various ways: if everyone is very certain of something, that pertains more to common sense than something people are less certain about. If some people express disagreement with a view, but everyone’s revealed preferences or beliefs indicate agreement, that can be said to pertain to common sense to some degree, but not so much as where verbal affirmations and revealed preferences and beliefs are aligned.

Naturally, all of this is a question of vague boundaries: opinions are more or less a matter of common sense. We cannot sort them into two clear categories of “common sense” and “not common sense.” Nonetheless, we would want to base our arguments, as much as possible, on things that are more squarely matters of common sense.

We can raise two questions about this. First, is it even possible? Second, why do it?

One might object that the proposal is impossible. For no one can really reason except from their own opinions. Otherwise, one might be formulating a chain of argument, but it is not one’s own argument or one’s own conclusion. But this objection is easily answered. In the first place, if everyone agrees on something, you probably agree yourself, and so reasoning from common sense will still be reasoning from your own opinions. Second, if you don’t personally agree, since belief is voluntary, you are capable of agreeing if you choose, and you probably should, for reasons which will be explained in answering the second question.

Nonetheless, the objection is a reasonable place to point out one additional qualification. “Everyone agrees with this” is itself a personal point of view that someone holds, and no one is infallible even with respect to this. So you might think that everyone agrees, while in fact they do not. But this simply means that you have no choice but to do the best you can in determining what is or what is not common sense. Of course you can be mistaken about this, as you can about anything.

Why argue from common sense? I will make two points, a practical one and a theoretical one. The practical point is that if your arguments are public, as for example this blog, rather than written down in a private journal, then you presumably want people to read them and to gain from them in some way. The more you begin from common sense, the more profitable your thoughts will be in this respect. More people will be able to gain from your thoughts and arguments if more people agree with the starting points.

There is also a theoretical point. Consider the statement, “The truth of a statement never makes a person more likely to utter it.” If this statement were true, no one could ever utter it on account of its truth, but only for other reasons. So it is not something that a seeker of truth would ever say. On the other hand, there can be no doubt that the falsehood of some statements, on some occasions, makes those statements more likely to be affirmed by some people. Nonetheless, the nature of language demands that people have an overall tendency, most of the time and in most situations, to speak the truth. We would not be able to learn the meaning of a word without it being applied accurately, most of the time, to the thing that it means. In fact, if everyone was always uttering falsehoods, we would simply learn that “is” means “is not,” and that “is not,” means “is,” and the supposed falsehoods would not be false in the language that we would acquire.

It follows that greater agreement that something is true, other things being equal, implies that the thing is more likely to be actually true. Stones have a tendency to fall down: so if we find a great collection of stones, the collection is more likely to be down at the bottom of a cliff rather than perched precisely on the tip of a mountain. Likewise, people have a tendency to utter the truth, so a great collection of agreement suggests something true rather than something false.

Of course, this argument depends on “other things being equal,” which is not always the case. It is possible that most people agree on something, but you are reasonably convinced that they are mistaken, for other reasons. But if this is the case, your arguments should depend on things that they would agree with even more strongly than they agree with the opposite of your conclusion. In other words, it should be based on things which pertain even more to common sense. Suppose it does not: ultimately the very starting point of your argument is something that everyone else agrees is false. This will probably be an evident insanity from the beginning, but let us suppose that you find it reasonable. In this case, Robin Hanson’s result discussed here implies that you must be convinced that you were created in very special circumstances which would guarantee that you would be right, even though no one else was created in these circumstances. There is of course no basis for such a conviction. And our ability to modify our priors, discussed there, implies that the reasonable behavior is to choose to agree with the priors of common sense, if we find our natural priors departing from them, except in cases where the disagreement is caused by agreement with even stronger priors of common sense. Thus for example in this post I gave reasons for disagreeing with our natural prior on the question, “Is this person lying or otherwise deceived?” in some cases. But this was based on mathematical arguments that are even more convincing than that natural prior.

Lies, Religion, and Miscalibrated Priors

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In a post from some time ago, Scott Alexander asks why it is so hard to believe that people are lying, even in situations where it should be obvious that they made up the whole story:

The weird thing is, I know all of this. I know that if a community is big enough to include even a few liars, then absent a strong mechanism to stop them those lies should rise to the top. I know that pretty much all of our modern communities are super-Dunbar sized and ought to follow that principle.

And yet my System 1 still refuses to believe that the people in those Reddit threads are liars. It’s actually kind of horrified at the thought, imagining them as their shoulders slump and they glumly say “Well, I guess I didn’t really expect anyone to believe me”. I want to say “No! I believe you! I know you had a weird experience and it must be hard for you, but these things happen, I’m sure you’re a good person!”

If you’re like me, and you want to respond to this post with “but how do you know that person didn’t just experience a certain coincidence or weird psychological trick?”, then before you comment take a second to ask why the “they’re lying” theory is so hard to believe. And when you figure it out, tell me, because I really want to know.

The strongest reason for this effect is almost certainly a moral reason. In an earlier post, I discussed St. Thomas’s explanation for why one should give a charitable interpretation to someone’s behavior, and in a follow up, I explained the problem of applying that reasoning to the situation of judging whether a person is lying or not. St. Thomas assumes that the bad consequences of being mistaken about someone’s moral character will be minor, and most of the time this is true. But if we asking the question, “are they telling the truth or are they lying?”, the consequences can sometimes be very serious if we are mistaken.

Whether or not one is correct in making this application, it is not hard to see that this is the principal answer to Scott’s question. It is hard to believe the “they’re lying” theory not because of the probability that they are lying, but because we are unwilling to risk injuring someone with our opinion. This is without doubt a good motive from a moral standpoint.

But if you proceed to take this unwillingness as a sign of the probability that they are telling the truth, this would be a demonstrably miscalibrated probability assignment. Consider a story on Quora which makes a good example of Scott’s point:

I shuffled a deck of cards and got the same order that I started with.

No I am not kidding and its not because I can’t shuffle.

Let me just tell the story of how it happened. I was on a trip to Europe and I bought a pack of playing cards at the airport in Madrid to entertain myself on the flight back to Dallas.

It was about halfway through the flight after I’d watched Pixels twice in a row (That s literally the only reason I even remembered this) And I opened my brand new Real Madrid Playing Cards and I just shuffled them for probably like 30 minutes doing different tricks that I’d learned at school to entertain myself and the little girl sitting next to me also found them to be quite cool.

I then went to look at the other sides of the cards since they all had a picture of the Real Madrid player with the same number on the back. That’s when I realized that they were all in order. I literally flipped through the cards and saw Nacho-Fernandes, Ronaldo, Toni Kroos, Karim Benzema and the rest of the team go by all in the perfect order.

Then a few weeks ago when we randomly started talking about Pixels in AP Statistics I brought up this story and my teacher was absolutely amazed. We did the math and the amount of possibilities when shuffling a deck of cards is 52! Meaning 52 x 51 x 50 x 49 x 48….

There were 8.0658175e+67 different combinations of cards that I could have gotten. And I managed to get the same one twice.

The lack of context here might make us more willing to say that Arman Razaali is lying, compared to Scott’s particular examples. Nonetheless, I think a normal person will feel somewhat unwilling to say, “he’s lying, end of story.” I certainly feel that myself.

It does not take many shuffles to essentially randomize a deck. Consequently if Razaali’s statement that he “shuffled them for probably like 30 minutes” is even approximately true, 1 in 52! is probably a good estimate of the chance of the outcome that he claims, if we assume that it happened by chance. It might be some orders of magnitude less since there might be some possibility of “unshuffling.” I do not know enough about the physical process of shuffling to know whether this is a real possibility or not, but it is not likely to make a significant difference: e.g. the difference between 10^67 and 10^40 would be a huge difference mathematically, but it would not be significant for our considerations here, because both are simply too large for us to grasp.

People demonstrably lie at far higher rates than 1 in 10^67 or 1 in 10^40. This will remain the case even if you ask about the rate of “apparently unmotivated flat out lying for no reason.” Consequently, “he’s lying, period,” is far more likely than “the story is true, and happened by pure chance.” Nor can we fix this by pointing to the fact that an extraordinary claim is a kind of extraordinary evidence. In the linked post I said that the case of seeing ghosts, and similar things, might be unclear:

Or in other words, is claiming to have seen a ghost more like claiming to have picked 422,819,208, or is it more like claiming to have picked 500,000,000?

That remains undetermined, at least by the considerations which we have given here. But unless you have good reasons to suspect that seeing ghosts is significantly more rare than claiming to see a ghost, it is misguided to dismiss such claims as requiring some special evidence apart from the claim itself.

In this case there is no such unclarity – if we interpret the claim as “by pure chance the deck ended up in its original order,” then it is precisely like claiming to have picked 500,000,000, except that it is far less likely.

Note that there is some remaining ambiguity. Razaali could defend himself by saying, “I said it happened, I didn’t say it happened by chance.” Or in other words, “but how do you know that person didn’t just experience a certain coincidence or weird psychological trick?” But this is simply to point out that “he’s lying” and “this happened by pure chance” are not exhaustive alternatives. And this is true. But if we want to estimate the likelihood of those two alternatives in particular, we must say that it is far more likely that he is lying than that it happened, and happened by chance. And so much so that if one of these alternatives is true, it is virtually certain that he is lying.

As I have said above, the inclination to doubt that such a person is lying primarily has a moral reason. This might lead someone to say that my estimation here also has a moral reason: I just want to form my beliefs in the “correct” way, they might say: it is not about whether Razaali’s story really happened or not.

Charles Taylor, in chapter 15 of A Secular Age, gives a similar explanation of the situation of former religious believers who apparently have lost their faith due to evidence and argument:

From the believer’s perspective, all this falls out rather differently. We start with an epistemic response: the argument from modern science to all-around materialism seems quite unconvincing. Whenever this is worked out in something closer to detail, it seems full of holes. The best examples today might be evolution, sociobiology, and the like. But we also see reasonings of this kind in the works of Richard Dawkins, for instance, or Daniel Dennett.

So the believer returns the compliment. He casts about for an explanation why the materialist is so eager to believe very inconclusive arguments. Here the moral outlook just mentioned comes back in, but in a different role. Not that, failure to rise to which makes you unable to face the facts of materialism; but rather that, whose moral attraction, and seeming plausibility to the facts of the human moral condition, draw you to it, so that you readily grant the materialist argument from science its various leaps of faith. The whole package seems plausible, so we don’t pick too closely at the details.

But how can this be? Surely, the whole package is meant to be plausible precisely because science has shown . . . etc. That’s certainly the way the package of epistemic and moral views presents itself to those who accept it; that’s the official story, as it were. But the supposition here is that the official story isn’t the real one; that the real power that the package has to attract and convince lies in it as a definition of our ethical predicament, in particular, as beings capable of forming beliefs.

This means that this ideal of the courageous acknowledger of unpalatable truths, ready to eschew all easy comfort and consolation, and who by the same token becomes capable of grasping and controlling the world, sits well with us, draws us, that we feel tempted to make it our own. And/or it means that the counter-ideals of belief, devotion, piety, can all-too-easily seem actuated by a still immature desire for consolation, meaning, extra-human sustenance.

What seems to accredit the view of the package as epistemically-driven are all the famous conversion stories, starting with post-Darwinian Victorians but continuing to our day, where people who had a strong faith early in life found that they had reluctantly, even with anguish of soul, to relinquish it, because “Darwin has refuted the Bible”. Surely, we want to say, these people in a sense preferred the Christian outlook morally, but had to bow, with whatever degree of inner pain, to the facts.

But that’s exactly what I’m resisting saying. What happened here was not that a moral outlook bowed to brute facts. Rather we might say that one moral outlook gave way to another. Another model of what was higher triumphed. And much was going for this model: images of power, of untrammelled agency, of spiritual self-possession (the “buffered self”). On the other side, one’s childhood faith had perhaps in many respects remained childish; it was all too easy to come to see it as essentially and constitutionally so.

But this recession of one moral ideal in face of the other is only one aspect of the story. The crucial judgment is an all-in one about the nature of the human ethical predicament: the new moral outlook, the “ethics of belief” in Clifford’s famous phrase, that one should only give credence to what was clearly demonstrated by the evidence, was not only attractive in itself; it also carried with it a view of our ethical predicament, namely, that we are strongly tempted, the more so, the less mature we are, to deviate from this austere principle, and give assent to comforting untruths. The convert to the new ethics has learned to mistrust some of his own deepest instincts, and in particular those which draw him to religious belief. The really operative conversion here was based on the plausibility of this understanding of our ethical situation over the Christian one with its characteristic picture of what entices us to sin and apostasy. The crucial change is in the status accorded to the inclination to believe; this is the object of a radical shift in interpretation. It is no longer the impetus in us towards truth, but has become rather the most dangerous temptation to sin against the austere principles of belief-formation. This whole construal of our ethical predicament becomes more plausible. The attraction of the new moral ideal is only part of this, albeit an important one. What was also crucial was a changed reading of our own motivation, wherein the desire to believe appears now as childish temptation. Since all incipient faith is childish in an obvious sense, and (in the Christian case) only evolves beyond this by being child-like in the Gospel sense, this (mis)reading is not difficult to make.

Taylor’s argument is that the arguments for unbelief are unconvincing; consequently, in order to explain why unbelievers find them convincing, he must find some moral explanation for why they do not believe. This turns out to be the desire to have a particular “ethics of belief”: they do not want to have beliefs which are not formed in such and such a particular way. This is much like the theoretical response above regarding my estimation of the probability that Razaali is lying, and how that might be considered a moral estimation, rather than being concerned with what actually happened.

There are a number of problems with Taylor’s argument, which I may or may not address in the future in more detail. For the moment I will take note of three things:

First, neither in this passage nor elsewhere in the book does Taylor explain in any detailed way why he finds the unbeliever’s arguments unconvincing. I find the arguments convincing, and it is the rebuttals (by others, not by Taylor, since he does not attempt this) that I find unconvincing. Now of course Taylor will say this is because of my particular ethical motivations, but I disagree, and I have considered the matter exactly in the kind of detail to which he refers when he says, “Whenever this is worked out in something closer to detail, it seems full of holes.” On the contrary, the problem of detail is mostly on the other side; most religious views can only make sense when they are not worked out in detail. But this is a topic for another time.

Second, Taylor sets up an implicit dichotomy between his own religious views and “all-around materialism.” But these two claims do not come remotely close to exhausting the possibilities. This is much like forcing someone to choose between “he’s lying” and “this happened by pure chance.” It is obvious in both cases (the deck of cards and religious belief) that the options do not exhaust the possibilities. So insisting on one of them is likely motivated itself: Taylor insists on this dichotomy to make his religious beliefs seem more plausible, using a presumed implausibility of “all-around materialism,” and my hypothetical interlocutor insists on the dichotomy in the hope of persuading me that the deck might have or did randomly end up in its original order, using my presumed unwillingness to accuse someone of lying.

Third, Taylor is not entirely wrong that such an ethical motivation is likely involved in the case of religious belief and unbelief, nor would my hypothetical interlocutor be entirely wrong that such motivations are relevant to our beliefs about the deck of cards.

But we need to consider this point more carefully. Insofar as beliefs are voluntary, you cannot make one side voluntary and the other side involuntary. You cannot say, “Your beliefs are voluntarily adopted due to moral reasons, while my beliefs are imposed on my intellect by the nature of things.” If accepting an opinion is voluntary, rejecting it will also be voluntary, and if rejecting it is voluntary, accepting it will also be voluntary. In this sense, it is quite correct that ethical motivations will always be involved, even when a person’s opinion is actually true, and even when all the reasons that make it likely are fully known. To this degree, I agree that I want to form my beliefs in a way which is prudent and reasonable, and I agree that this desire is partly responsible for my beliefs about religion, and for my above estimate of the chance that Razaali is lying.

But that is not all: my interlocutor (Taylor or the hypothetical one) is also implicitly or explicitly concluding that fundamentally the question is not about truth. Basically, they say, I want to have “correctly formed” beliefs, but this has nothing to do with the real truth of the matter. Sure, I might feel forced to believe that Razaali’s story isn’t true, but there really is no reason it couldn’t be true. And likewise I might feel forced to believe that Taylor’s religious beliefs are untrue, but there really is no reason they couldn’t be.

And in this respect they are mistaken, not because anything “couldn’t” be true, but because the issue of truth is central, much more so than forming beliefs in an ethical way. Regardless of your ethical motives, if you believe that Razaali’s story is true and happened by pure chance, it is virtually certain that you believe a falsehood. Maybe you are forming this belief in a virtuous way, and maybe you are forming it in a vicious way: but either way, it is utterly false. Either it in fact did not happen, or it in fact did not happen by chance.

We know this, essentially, from the “statistics” of the situation: no matter how many qualifications we add, lies in such situations will be vastly more common than truths. But note that something still seems “unconvincing” here, in the sense of Scott Alexander’s original post: even after “knowing all this,” he finds himself very unwilling to say they are lying. In a discussion with Angra Mainyu, I remarked that our apparently involuntary assessments of things are more like desires than like beliefs:

So rather than calling that assessment a belief, it would be more accurate to call it a desire. It is not believing something, but desiring to believe something. Hunger is the tendency to go and get food; that assessment is the tendency to treat a certain claim (“the USA is larger than Austria”) as a fact. And in both cases there are good reasons for those desires: you are benefited by food, and you are benefited by treating that claim as a fact.

In a similar way, because we have the natural desire not to injure people, we will naturally desire not to treat “he is lying” as a fact; that is, we will desire not to believe it. The conclusion that Angra should draw in the case under discussion, according to his position, is that I do not “really believe” that it is more likely that Razaali is lying than that his story is true, because I do feel the force of the desire not to say that he is lying. But I resist that desire, in part because I want to have reasonable beliefs, but most of all because it is false that Razaali’s story is true and happened by chance.

To the degree that this desire feels like a prior probability, and it does feel that way, it is necessarily miscalibrated. But to the degree that this desire remains nonetheless, this reasoning will continue to feel in some sense unconvincing. And it does in fact feel that way to me, even after making the argument, as expected. Very possibly, this is not unrelated to Taylor’s assessment that the argument for unbelief “seems quite unconvincing.” But discussing that in the detail which Taylor omitted is a task for another time.