In “What is Evidence?” I wrote:1
This is why rationalists put such a heavy premium on the paradoxical-seeming claim that a belief is only really worthwhile if you could, in principle, be persuaded to believe otherwise. If your retina ended up in the same state regardless of what light entered it, you would be blind . . . Hence the phrase, “blind faith.” If what you believe doesn’t depend on what you see, you’ve been blinded as effectively as by poking out your eyeballs.
Cihan Baran replied:2
I can not conceive of a situation that would make 2 + 2 = 4 false. Perhaps for that reason, my belief in 2 + 2 = 4 is unconditional.
I admit, I cannot conceive of a “situation” that would make 2 + 2 = 4 false. (There are redefinitions, but those are not “situations,” and then you’re no longer talking about 2, 4, =, or +.) But that doesn’t make my belief unconditional. I find it quite easy to imagine a situation which would convince me that 2 + 2 = 3.
Suppose I got up one morning, and took out two earplugs, and set them down next to two other earplugs on my nighttable, and noticed that there were now three earplugs, without any earplugs having appeared or disappeared—in contrast to my stored memory that 2 + 2 was supposed to equal 4. Moreover, when I visualized the process in my own mind, it seemed that making xx and xx come out to xxxx required an extra x to appear from nowhere, and was, moreover, inconsistent with other arithmetic I visualized, since subtracting xx from xxx left xx, but subtracting xx from xxxx left xxx. This would conflict with my stored memory that 3 - 2 = 1, but memory would be absurd in the face of physical and mental confirmation that xxx - xx = xx.
I would also check a pocket calculator, Google, and perhaps my copy of 1984 where Winston writes that “Freedom is the freedom to say two plus two equals three.” All of these would naturally show that the rest of the world agreed with my current visualization, and disagreed with my memory, that 2 + 2 = 3.
How could I possibly have ever been so deluded as to believe that 2 + 2 = 4? Two explanations would come to mind: First, a neurological fault (possibly caused by a sneeze) had made all the additive sums in my stored memory go up by one. Second, someone was messing with me, by hypnosis or by my being a computer simulation. In the second case, I would think it more likely that they had messed with my arithmetic recall than that 2 + 2 actually equalled 4. Neither of these plausible-sounding explanations would prevent me from noticing that I was very, very, very confused.3
What would convince me that 2 + 2 = 3, in other words, is exactly the same kind of evidence that currently convinces me that 2 + 2 = 4: The evidential crossfire of physical observation, mental visualization, and social agreement.
There was a time when I had no idea that 2 + 2 = 4. I did not arrive at this new belief by random processes—then there would have been no particular reason for my brain to end up storing “2 + 2 = 4” instead of “2 + 2 = 7.” The fact that my brain stores an answer surprisingly similar to what happens when I lay down two earplugs alongside two earplugs, calls forth an explanation of what entanglement produces this strange mirroring of mind and reality.
There’s really only two possibilities, for a belief of fact—either the belief got there via a mind-reality entangling process, or not. If not, the belief can’t be correct except by coincidence. For beliefs with the slightest shred of internal complexity (requiring a computer program of more than 10 bits to simulate), the space of possibilities is large enough that coincidence vanishes.4
Unconditional facts are not the same as unconditional beliefs. If entangled evidence convinces me that a fact is unconditional, this doesn’t mean I always believed in the fact without need of entangled evidence.
I believe that 2 + 2 = 4, and I find it quite easy to conceive of a situation which would convince me that 2 + 2 = 3. Namely, the same sort of situation that currently convinces me that 2 + 2 = 4. Thus I do not fear that I am a victim of blind faith.5
1See Map and Territory.
2Comment: http://lesswrong.com/lw/jl/what_is_evidence/f7h.
3See “Your Strength as a Rationalist” in Map and Territory.
4For more on belief formation and beliefs of fact, see “Feeling Rational” and “What Is Evidence?” in Map and Territory. For more on belief complexity, see “Occam’s Razor” in the same volume.
5If there are any Christians reading this who know Bayes’s Theorem, might I inquire of you what situation would convince you of the truth of Islam? Presumably it would be the same sort of situation causally responsible for producing your current belief in Christianity: We would push you screaming out of the uterus of a Muslim woman, and have you raised by Muslim parents who continually told you that it is good to believe unconditionally in Islam.
Or is there more to it than that? If so, what situation would convince you of Islam, or at least, non-Christianity? And how confident are you that the general kinds of evidence and reasoning you appeal to would have been enough to dissuade you of your religion if you had been raised a Muslim?
I see a lot of people arguing that "2", "3", "+", and "=" are defined in terms of the Peano axioms, and as such, aren't actually relevant to the behavior of physical objects. They say that the axioms pin down the numbers, regardless of how physical objects behave or start behaving.
But the Peano axioms use something called a "successor" to generate the natural numbers. And how do we figure out what the successors are? Well, one notation is to append an "S" to the previous number to indicate that number's successor, such that the successor of "SS0" is "SSS0". Then "+" would mean "repeatedly apply the successor operation to the number to the right of this operator for however many times indicated by the number to the left of this operator", and "=" would indicate "these two numbers, when written out using successor-notation, have the character 'S' occur the same number of times".
So how do we calculate "2 + 2"? Well, we take the number of occurrences of the character "S", count them up, then put the total number of occurrences in front of a single "0": "SSSS0", which we interpret as "4". "2 + 2 = 4".
But now let's imagine your brain's visual cortex (or whatever it uses to visualize things) being messed up somehow. Actually, let's go further than that, and suppose everyone's visual cortexes got messed up in the same way, so that now, when we visualize two objects and two more objects, and put them together, we see, not four objects, but three. So if you were to try and visualize a group of two dots coming together with another group of two dots, you would end up seeing, in your mind's eye, a final group of three dots.
Now imagine counting the number of times "S" occurs in "SS0", then putting two of those groups of "S" characters together. How many "S" character are in the final group? Visualize it, now...
Why, three. Of course there's three. If you take "SS" and put it with "SS", of course you get "SSS". What's that? You say you're getting "SSSS"? Where are you getting that extra "S" from? What? No--can't you see it? It's obviously three--how can you put those two groups together and get four?
So, "SS0 + SS0 = SSS0".
My point is this: you can't just point to the Peano axioms and say, "Ha! Your hypothetical situation involving the behavior of mere physical objects is meaningless before the might of my absolute mathematical assumptions!" Remember, when you try to perform "logic" on those axioms, you're still using your brain to do it. And however ivory-tower untouchable you imagine your axioms to be, your brain is a real, physical object performing real physical computations. If we lived in a slightly different universe, your brain would take one look at "SS0" and "SS0", visually add together the number of "S" characters, and see "SSS0". Anyone who saw "SSSS0" would be seen as crazy, or brain-damaged, or something.
Physics trumps math and logic.
Not sure who "they" are. May I suggest reading up on model theory? Maybe Enderton's "mathematical logic" (?).
It's important to think separately about the "model" (the thing we are studying), the "language" (where we make statements about the model), and the "theory" (a set of statements in a language). The same theory in a particular language may and in fact generally does apply to multiple dis... (read more)