I never really understood the concept of the individual i.e. an indivisible person. I always felt divisible, something like a Freudian superego/ego/id, but clearly when I face the dilemma of sticking to weight loss or eating a cake, it is not one indivisible person making a choice, but two agents arguing with each other inside me. It is more or less literally heard as an internal dialogue. Not for everybody?
I am fighting an ugly case of alcohol addiction. There is the Higher Self, the one with the low time preference, who wants to live in a healthy and a rational way until 75, and the Lower Self, who wants to indulge in every impulse now, and does not care if it dies at 50. I used to do what I guess is the common case, identify with the Higher Self, as it is far more respectable and feels good to identify with it, and consider the lower self an external demon. However, this means always having to fight the demon. And that is tiresome. So I turned it around, identified with the lower self, and basically accepted I am a pig with poor impulse control, and turned the Higher Self into an exterrnal entity I call The Boss. The advantage is that instead of fighting The Demon, it is now surrendering to The Boss. So it feels like I really want a drink, but cannot, because The Boss forbade it, and no use in fighting The Boss. Surrendering to an externalized internal agent is easier than fighting it. Later on I realized I basically reinvented half of AA's 12-step program as they too build on a surrender to a higher being.
My point is to me the bicameral mind does not even feel weird, I am doing something like that on a daily basis, I just wonder why not everybody, and the only thing that feels weird about it is why only two? It is easy to have 3-4 conflicting ideas generating 3-4 conflicting sub-agents fighting it out. It is like in multithreaded programming, where every important function gets its own thread, every important idea gets an amount of selfhood, agency invested into it.
I am not sure that it is productive to tell certain people that they do not really believe what they claim to believe, and that they only believe they believe it. I have an alternative suggestion that could possibly be more useful.
Binary Beliefs
It seems that human beings have two kinds of beliefs: binary beliefs and quasi-Bayesian beliefs. The binary beliefs are what we usually think of as beliefs, simple statements which are true or false like "Two and two make four," "The sun will rise tomorrow," "The Messiah is coming," and so on.
Binary beliefs are basically voluntary. We can choose such beliefs much as we can choose to lift our arms and legs. If I say "the sun will rise tomorrow," I am choosing to say this, just as I can choose to lift my arm. I can even choose the internal factor. I can choose to say to myself, "the sun will rise tomorrow." And I can also choose to say that the sun will NOT rise. I can choose to say this to others, and I can even choose to say it to myself, within my own head.
Of course, it would be reasonable to respond to this by saying that this does not mean that someone can choose to believe that the sun will not rise. Even if he says this to himself, he still does not act as though the sun is not going to rise. He won't start making preparations for a freezing world, for example. The answer to this is that choosing to believe something is more than choosing to say it to oneself and to others. Rather, it is choosing to conform the whole of one's life to the idea that this is true. And someone could indeed choose to believe that the sun will not rise in this sense, if he thought he had a reason to do so. If he did so choose, he would indeed begin to make preparations for a dark world, because he would be choosing to conform his actions to that opinion. And he would do this voluntarily, just as someone can voluntarily lift his arm.
Quasi-Bayesian Beliefs
At the same time, human beings have quasi-Bayesian beliefs. These are true degrees of belief like probabilities, never really becoming absolutely certain of the truth or falsity of anything, but sometimes coming very close. These are internal estimates of the mind, and are basically non-voluntary. Instead of depending on choice, they actually depend on evidence, although they are influenced by other factors as well. A person cannot choose to increase or decrease this estimate, although he can go and look for evidence. On account of the flawed nature of the mind, if someone only looks for confirming evidence and ignores disconfirming evidence, this estimate in principle can go very high even when the objective state of the evidence does not justify this.
Belief in Belief
It seems to me that what we usually call belief in belief basically means that someone holds a binary belief together with a quasi-Bayesian belief which conflicts with it. So he says "The Messiah is coming," saying it to himself and others, and in every way acting as though this is true, even though his internal Bayesian estimate is that after all these thousands of years, the evidence is strongly against this. So he has a positive binary belief while having a very low estimate of the probability of this belief.
The reason why this often happens with religion in particular is that religious beliefs very often do not have huge negative consequences if they are mistaken. In principle, someone can choose to believe that if he jumps from the window of the tenth story of a building, he will be ok. In practice, no one will choose this on account of his non-voluntary Bayesian estimate that he is very likely to be hurt if does so. But a person does not notice much harm from believing the Messiah is coming, and so he can choose to believe it even if his internal estimate says that it is likely to be false.
A cautionary note: one might be tempted to think that religious people in general have belief in belief in this sense, that they all really know that their religions are unlikely to be true. This is not the case. There are plenty of ways to distort the internal estimate, even though one cannot directly choose this estimate. I know many very religious people who clearly have an extremely high internal estimate of the truth of their religion. They REALLY BELIEVE it is true, in the fullest possible sense. But on the other hand I also know others, also extremely devout, who clearly have an internal estimate which is extremely low: they are virtually certain that their religion is false, and yet in every way, externally and internally, they act and think as though it were true.