The piece about tautologies having to be empirically observed is one of the most bizarre posts I’ve ever read by you. It is so strange that I’m not really sure if there is anything I can say that would change you mind if you really think you could be convinced that 2+2=3 in that way. I can’t even tell where you went wrong. Do you also hold that that the identity relation has to be empirically observed? Could you be convinced that 4=3? That 3 doesn’t = 3? Do you believe you could be convinced that triangles on Euclidean planes are round? Do you not trust modus ponens and modus tollens? How does one even empirically observe tautologies in symbolic logic?
That 2+2=4 is a fact about a mathematical system that exists independently of the physical universe, including us humans that decided to use those symbols to express that fact. That fact is in the territory. But, in order to interact with the physical universe, it has to be discovered by some physical system that explores logical conclusions, such as our brains. This exploration builds our map of the territory. Our uncertainty about the tautological statement does not reflect some vagueness in the territory of logic, but our uncertainty about the workings of our physical brains, and their ability to build maps that reflect the territory.
Problems of logic have 100% correct answers, but our physical brains cannot become 100% entangled with those correct answers. It is observation, which can be abstract observations of our own logical reasoning, which give us increasing entanglement which approaches, but never reaches, 100%.
Whatever you could possibly know and value about reality can only exist independently of the physical universe. (Huh?) If your uncertainty about math doesn’t indicate uncertainty of the math, and it’s an argument for math being otherworldly, it’s also an argument for the territory being otherworldly, which is clearly a confusion of terms.
And so you should bring the math back where it belongs, an aspect of the territory.
Whatever you could possibly know and value about reality can only exist independently of the physical universe.
That is not what I am saying. I mean that things that we think of as tautologies, or purely logical truths, which are true no matter what universe we are in, exist independently of the physical universe. Facts about the physical universe are not in this class. Indeed, the entanglement of our physical brains with these logical truths is an example of a fact about the physical universe that, of course, depends on the the universe.
If your uncertainty about math doesn’t indicate uncertainty of the math, and it’s an argument for math being otherworldly...
You have my argument backwards. I first make the point that facts about math are not facts about the physical universe to support that the uncertainty we have about math, which exists in our heads, in our physical universe, does not exist in math itself. The argument does not work the other way, there are plenty of instances of uncertainty in our minds that are not uncertainty in the things elsewhere in the physical universe that they are about.
My comment was an attempt to explain why we need observation to believe things that are objectively true regardless of the world we exists in. Basically, we need evidence that our brains, existing in the physical worlds, are suitable for representing the logical truths.
This is really helpful and I think I agree with all of it. I’ve just never understood “observation” to include my logical reasoning. If your position is that we know 2+2=4 by virtue of observing our own reasoning and not by virtue of any sensory data (information about the outside world) then I don’t think that position is any different from the one I already hold. But is this Eliezer’s position? His OB post made it sound like he could be swayed to think 2+2=3 as a result of external events mediated by his sensory perception of those events. That is what I objected to.
Well, I think that observations can be both our reasoning and sensory data.
Suppose you have a model* of your own accuracy at addition of integers, which is that you are 95% likely to get the correct answer, 2% to be one high, 2% to be one low, and with the remaining 1% divided somehow amongst other possibilities. Then, when you actually observe that when adding 2 + 2 you get 4, this is Bayesian evidence that gives a likelihood ratio of 42.5 : 1 in favor of the theory that 2 + 2 = 4 compared to the theory that 2 + 2 = 3.
Now suppose you have a collection of pebbles, and your model of the pebbles claims that if you count out 2 distinct collections of pebbles, and then combine them and count the total, that the sum of the counts of the distinct collections is 90% likely to be the count of the combined collection, and is 4% likely to be one high, 4% to be one low, and 2% to be something else. And then you actually count out a collection of 2 pebbles, and another collection of 2 pebbles, and combine them, and when you count the combined collection you count 4 pebbles. This is Bayesian evidence with a likelihood ratio of 22.5 : 1 in favor of 2 + 2 = 4 as opposed to 2 + 2 = 3.
In both cases, belief in a logical proposition results from our belief that an observable system has some probability of reflecting logical truth. If, as in the example numbers that I made up just now, we believe that our reasoning process is more likely than observations of our environment, then the results of our reasoning is stronger evidence, but it is still the same class of evidence.
* I have neglected the harder problem of simultaneously updating propositions about additions and propositions about a given system’s probability of representing addition. That is, I have not explained where the models I asked you suppose you have really should come from.
Thanks. That is worth noting. My recollection is that Quine denies the existence of analytic statements but doesn’t go as far as to hold that tautological statements are just like regular empirical statements. Logical truths still have some kind of special status for Quine. Plus, I think his reasons for denying analytic truths had very little to do with actually being able to imagine a series of experiences that could change his mind about them– it is one thing to claim that such experiences are possible. Its another thing to claim you have just described that set of experiences.
Finally, I remember thinking Quine was being silly, but it has been a while so I’m going to go read and come back.
I don’t think I’d read Eliezer’s piece about tautologies having to be observed before, but it matches my pre-existing beliefs about its topic, and it seems so obvious that I’m left wondering how you think you got the understanding that 2+2=4, or that triangles on Euclidean planes are not round. Given that you got that understanding somehow, couldn’t the same process give you the new understanding, assuming (for this argument) it was true?
This is certainly a strange divergence of intuitions. I think the story of how I came to know 2+2=4 goes like this: Someone taught me that 2 meant -oo- and 4 meant -oooo-. Then someone probably be told me that 2+2=4 but I don’t think they would have needed to. I think I could easily have come to the conclusion myself since given -oo- and -oo- I can count four dots. If pushing four objects together meant one of the objects disappeared I would probably just stop pushing objects together and count in my head. If counting the objects made one of them disappear I would be pretty damn frustrated but I’m pretty confident I could realize that reality was changing as a result of a mental operation and not that I was counting wrong. Aside from being tortured with rats or Cardassian pain sticks I don’t see what would make me think that 2+2 didn’t =4.
I’m not sure how to explain my thinking any better except to say that it is the same thinking that lead generations of philosophers and mathematicians to conclude that mathematical knowledge was a different kind of knowledge than knowledge of our surrounding and the natural world. My reason is the reason Kant distinguished the analytic from the synthetic- a sense that a rational mind could figure these things out without sensory input.
The trouble there is the claim of a rational mind, in my opinion. It’s not logically necessary that our evolved brains, hacked by culture, are going to mirror reality in their most basic perceptions and intuitions.
The space of all possible minds includes some which have a notion of number and counting and an intuitive mental arithmetic, but for which 2 and 2 really do seem to make 3 when they think of it. These minds, of course, would notice empirical contradictions everywhere: they would put two objects together with two more, count them, and count four instead of three, when it’s obvious by visualizing in their heads that two and two make three instead. Eventually, a sufficiently reflective mind of this type would entertain the possibility that maybe two and two do actually make four, and that its system of visualization and mental arithmetic are in fact wrong, as obvious as they seem from the inside. Switching “three” and “four” in this paragraph just illustrates how difficult accepting that hypothesis might actually be for such a mind.
The thing is, we ourselves are in this situation, not with arithmetic (fortunately, we receive constant empirical reinforcement that 2+2=4 and that our mental faculties for arithmetic work properly) but with our biases of thought. Things like our preferences and valuations seem to be rational and coherent, in that we can usually defend them all with arguments that look solid and persuasive to us. But occasionally this fiction becomes untenable, as when we are shown to have circular preferences in situations of risk and reward. As Eliezer put it in Zut Allais:
You want to scream, “Just give up already! Intuition isn’t always right!”
Or, in this case, “Don’t start by assuming that our minds work rationally whenever they see something as obvious! If this is true, it is an empirical fact; and you should be able to see the alternative as possible!”
If this is true, it is an empirical fact; and you should be able to see the alternative as possible!
Indeed, 2+2=4 is only true in some contexts. For example, sometimes 1+1=1 -- in contexts where separate objects lose their distinct identity as soon as they are grouped. (Think of a particular object several times. How many times did you think of it? But how many objects did you think of?)
Later edit: It is interesting that such a benign comment would get 4 down votes. Perhaps I understand this group well enough to guess why: the experiment I suggested is an entirely “internal” one, it provides no external proof of what I am suggesting. I think that a common reader here feels dismissive of, if not entirely antagonistically towards, knowledge that is internally generated. Personally, I have a preference for the knowledge that arises from internal experience.
I agree that the downvoting of this comment was overly harsh. My theory on why it occurred is different, and best illustrated by an example: if someone posted a comment saying “2+2=4 is only true in some contexts; in arithmetic modulo 3, 2+2=1”, that comment would have been similarly downvoted.
However, let me be so bold as to say a word in defense of even that hypothetical commenter. Anyone mathematically sophisticated (including our downvoters) will agree that it is possible to construct a mathematical system in which 2+2 equals anything you like—or, more precisely, for any symbol x, a system can be constructed in which the formula (string of symbols) “2+2 = x” is given the label “TRUE”. Mod 3 arithmetic is an example for x = “1”.
Now, it is at this point that the downvoters protest: “But this is not the same thing as saying 2+2=1! All you’ve done is change the meaning of the symbols in the formula, such as ‘2’ and ‘1’. Two plus two is still four, for the original meaning of those words. You’re confusing the map and the territory. Downvoted!”
Well, the downvoters do have a point. But, at the same time, let me suggest that they’re also making the same mistake as our poor beleaguered commenter!
What they’ve done, you see, is to make a leap from “Ordinary (i.e. non mod-3, etc.) Arithmetic accurately models certain physical phenomena” to something like “Ordinary Arithmetic is true in (or of) the physical world”. Instead of saying what they mean, which is “the physical world is best modeled by a system that has ‘2+2=4’ as a ‘TRUE’ formula”, they say “2+2 is in fact equal to 4″.
Small wonder that confusion arises about whether mathematical statements are “emprical” or not! “The physical world is best modeled by a system that has ‘2+2=4’ as a ‘TRUE’ formula” is clearly an empirical claim. But what about 2+2 = 4, all by itself? When a mathematician at a blackboard proves that 2+2=4 in Ordinary Arithmetic (or, for Eliezer’s benefit, that infinite sets exist in standard set theory), has he or she made a claim about physics? No! Not without the additional assumption that the formal system being used is in fact an accurate map of the territory! But the mathematician makes no such assumption; he or she (acting as a mathematician) is interested only in the properties of formal systems. (Yes, that’s right: I’m advocating the view known as formalism here. The other well-known positions in the philosophy of mathematics, namely Platonism and intuitionism, suffer from map-territory confusion!)
Mathematical systems, like Ordinary Arithmetic or Mod-3 Arithmetic, are part of the map, not the territory. The facts of mathematics are, so to speak, cartographic, rather than geographic.
In the OB post tautologies have to be empirically observed somehow, Eliezer writes about waking up one day and discovering all sorts of evidence that 2+2=3. This wouldn’t be evidence that 2+2=3 in Peano arithmetic, it would be evidence that Peano arithmetic just doesn’t apply for some reason. In my down-voted comment, I was just giving an example of how there can be different kinds of arithmetic if you are willing to be flexible about what arithmetic is. (If you are not willing to be flexible, then you are not willing to allow the observation that 2+2=3 as an observation about arithmetic, because this is not possibly true in standard arithmetic. Well, the observations are possible but you’d have to account for it as some kind of grand delusion.) My point is that 2+2=4 in Peano Arithmetic independent of observation, but observation tells you if Peano arithmetic applies or not.
This wouldn’t be evidence that 2+2=3 in Peano arithmetic, it would be evidence that Peano arithmetic just doesn’t apply for some reason.
Exactly.
My point is that 2+2=4 in Peano Arithmetic independent of observation, but observation tells you if Peano arithmetic applies or not.
It is worth emphasizing that to claim that “2+2=4 in Peano Arithmetic independent of observation” is not to claim that our knowledge of this fact about Peano Arithmetic is independent of observation. (The former claim is about our map of the territory; the latter is about our map of our map of the territory.)
It is worth emphasizing that to claim that “2+2=4 in Peano Arithmetic independent of observation” is not to claim that our knowledge of this fact about Peano Arithmetic is independent of observation. (The former claim is about our map of the territory; the latter is about our map of our map of the territory.)
Could you elaborate? It sounds to me like the former claim is about the territory, and the latter is just hard for me to parse.
I’ll emphasize with the following analogy: you need to observe the sun to know of it. However, you can nevertheless be certain—as certain as you are of anything at all—that the sun exists independently of observation. You need to define the Peano axioms and observe the deductions that lead to the tautologies to know of them, but they are mathematically true independent of your observation.
Saying that 2+2=4 is a tautology in a certain axiomatic system defined with ‘+’ means that you couldn’t have anything but 2+2=4 in that system. It’s simply mandatory, and a rational person could not wake up one day and be convinced that 2+2=3 within a self-consistent system that deduces 2+2=4.
While tautological truth is independent of observation (let’s call it mathematical truth), it is dependent upon context (i.e., a self-consistent axiomatic system). Some mathematical truths in one axiomatic system are false in another. When we talk about whether a a mathematical statement is true, we need to specify the context, and, in my opinion, in the most demanding definition of truth, the context is the real, actual, empirical world. So I agree with Eliezer that a mathematical tautology must be observed in order to be true.
When we humans talk about “2+2=4”, it is because we have chosen arithmetic from an infinite number of possible axiomatic systems and given it a name and a set of agreed-upon symbols. Why did we do that? Because we observed arithmetic empirically. Obviously, addition is just one operation of infinitely many operations. The ones we have defined (multiplication, subtraction, addition mod n, taking the cardinality of subsets of, etc.) usually have some empirical relevance. While we don’t feel very comfortable thinking of those that don’t (and this says somethng about the way we think), I have faith that if we were presented with a very strange set of observations, it would take a pretty short amount of time to train ourselves to think of the new operation as a “natural” one.
… I idly wonder if there is a such thing as a mathematical truth that could not be realized empirically, in any context, and if there would be any way of deducing it’s non-feasability.
Is saying “we could have a different axiomatic system” different from saying “2, 4, +, and = could all mean different things? Of course we’ve only defined the operations and terms that are useful to us. I don’t care about the naturalness of ‘+’ only that once I know the meaning of the operations and terms the answer is obvious and indisputable.
Math isn’t my field, so my all means show me how I’m wrong.
The piece about tautologies having to be empirically observed is one of the most bizarre posts I’ve ever read by you. It is so strange that I’m not really sure if there is anything I can say that would change you mind if you really think you could be convinced that 2+2=3 in that way. I can’t even tell where you went wrong. Do you also hold that that the identity relation has to be empirically observed? Could you be convinced that 4=3? That 3 doesn’t = 3? Do you believe you could be convinced that triangles on Euclidean planes are round? Do you not trust modus ponens and modus tollens? How does one even empirically observe tautologies in symbolic logic?
That 2+2=4 is a fact about a mathematical system that exists independently of the physical universe, including us humans that decided to use those symbols to express that fact. That fact is in the territory. But, in order to interact with the physical universe, it has to be discovered by some physical system that explores logical conclusions, such as our brains. This exploration builds our map of the territory. Our uncertainty about the tautological statement does not reflect some vagueness in the territory of logic, but our uncertainty about the workings of our physical brains, and their ability to build maps that reflect the territory.
Problems of logic have 100% correct answers, but our physical brains cannot become 100% entangled with those correct answers. It is observation, which can be abstract observations of our own logical reasoning, which give us increasing entanglement which approaches, but never reaches, 100%.
Whatever you could possibly know and value about reality can only exist independently of the physical universe. (Huh?) If your uncertainty about math doesn’t indicate uncertainty of the math, and it’s an argument for math being otherworldly, it’s also an argument for the territory being otherworldly, which is clearly a confusion of terms.
And so you should bring the math back where it belongs, an aspect of the territory.
That is not what I am saying. I mean that things that we think of as tautologies, or purely logical truths, which are true no matter what universe we are in, exist independently of the physical universe. Facts about the physical universe are not in this class. Indeed, the entanglement of our physical brains with these logical truths is an example of a fact about the physical universe that, of course, depends on the the universe.
You have my argument backwards. I first make the point that facts about math are not facts about the physical universe to support that the uncertainty we have about math, which exists in our heads, in our physical universe, does not exist in math itself. The argument does not work the other way, there are plenty of instances of uncertainty in our minds that are not uncertainty in the things elsewhere in the physical universe that they are about.
My comment was an attempt to explain why we need observation to believe things that are objectively true regardless of the world we exists in. Basically, we need evidence that our brains, existing in the physical worlds, are suitable for representing the logical truths.
This is really helpful and I think I agree with all of it. I’ve just never understood “observation” to include my logical reasoning. If your position is that we know 2+2=4 by virtue of observing our own reasoning and not by virtue of any sensory data (information about the outside world) then I don’t think that position is any different from the one I already hold. But is this Eliezer’s position? His OB post made it sound like he could be swayed to think 2+2=3 as a result of external events mediated by his sensory perception of those events. That is what I objected to.
Well, I think that observations can be both our reasoning and sensory data.
Suppose you have a model* of your own accuracy at addition of integers, which is that you are 95% likely to get the correct answer, 2% to be one high, 2% to be one low, and with the remaining 1% divided somehow amongst other possibilities. Then, when you actually observe that when adding 2 + 2 you get 4, this is Bayesian evidence that gives a likelihood ratio of 42.5 : 1 in favor of the theory that 2 + 2 = 4 compared to the theory that 2 + 2 = 3.
Now suppose you have a collection of pebbles, and your model of the pebbles claims that if you count out 2 distinct collections of pebbles, and then combine them and count the total, that the sum of the counts of the distinct collections is 90% likely to be the count of the combined collection, and is 4% likely to be one high, 4% to be one low, and 2% to be something else. And then you actually count out a collection of 2 pebbles, and another collection of 2 pebbles, and combine them, and when you count the combined collection you count 4 pebbles. This is Bayesian evidence with a likelihood ratio of 22.5 : 1 in favor of 2 + 2 = 4 as opposed to 2 + 2 = 3.
In both cases, belief in a logical proposition results from our belief that an observable system has some probability of reflecting logical truth. If, as in the example numbers that I made up just now, we believe that our reasoning process is more likely than observations of our environment, then the results of our reasoning is stronger evidence, but it is still the same class of evidence.
* I have neglected the harder problem of simultaneously updating propositions about additions and propositions about a given system’s probability of representing addition. That is, I have not explained where the models I asked you suppose you have really should come from.
It may be worth noting that Quine had a view similar to Eliezer’s—which Stove alludes to (dismissively) in the essay.
Thanks. That is worth noting. My recollection is that Quine denies the existence of analytic statements but doesn’t go as far as to hold that tautological statements are just like regular empirical statements. Logical truths still have some kind of special status for Quine. Plus, I think his reasons for denying analytic truths had very little to do with actually being able to imagine a series of experiences that could change his mind about them– it is one thing to claim that such experiences are possible. Its another thing to claim you have just described that set of experiences.
Finally, I remember thinking Quine was being silly, but it has been a while so I’m going to go read and come back.
I don’t think I’d read Eliezer’s piece about tautologies having to be observed before, but it matches my pre-existing beliefs about its topic, and it seems so obvious that I’m left wondering how you think you got the understanding that 2+2=4, or that triangles on Euclidean planes are not round. Given that you got that understanding somehow, couldn’t the same process give you the new understanding, assuming (for this argument) it was true?
This is certainly a strange divergence of intuitions. I think the story of how I came to know 2+2=4 goes like this: Someone taught me that 2 meant -oo- and 4 meant -oooo-. Then someone probably be told me that 2+2=4 but I don’t think they would have needed to. I think I could easily have come to the conclusion myself since given -oo- and -oo- I can count four dots. If pushing four objects together meant one of the objects disappeared I would probably just stop pushing objects together and count in my head. If counting the objects made one of them disappear I would be pretty damn frustrated but I’m pretty confident I could realize that reality was changing as a result of a mental operation and not that I was counting wrong. Aside from being tortured with rats or Cardassian pain sticks I don’t see what would make me think that 2+2 didn’t =4.
I’m not sure how to explain my thinking any better except to say that it is the same thinking that lead generations of philosophers and mathematicians to conclude that mathematical knowledge was a different kind of knowledge than knowledge of our surrounding and the natural world. My reason is the reason Kant distinguished the analytic from the synthetic- a sense that a rational mind could figure these things out without sensory input.
The trouble there is the claim of a rational mind, in my opinion. It’s not logically necessary that our evolved brains, hacked by culture, are going to mirror reality in their most basic perceptions and intuitions.
The space of all possible minds includes some which have a notion of number and counting and an intuitive mental arithmetic, but for which 2 and 2 really do seem to make 3 when they think of it. These minds, of course, would notice empirical contradictions everywhere: they would put two objects together with two more, count them, and count four instead of three, when it’s obvious by visualizing in their heads that two and two make three instead. Eventually, a sufficiently reflective mind of this type would entertain the possibility that maybe two and two do actually make four, and that its system of visualization and mental arithmetic are in fact wrong, as obvious as they seem from the inside. Switching “three” and “four” in this paragraph just illustrates how difficult accepting that hypothesis might actually be for such a mind.
The thing is, we ourselves are in this situation, not with arithmetic (fortunately, we receive constant empirical reinforcement that 2+2=4 and that our mental faculties for arithmetic work properly) but with our biases of thought. Things like our preferences and valuations seem to be rational and coherent, in that we can usually defend them all with arguments that look solid and persuasive to us. But occasionally this fiction becomes untenable, as when we are shown to have circular preferences in situations of risk and reward. As Eliezer put it in Zut Allais:
Or, in this case, “Don’t start by assuming that our minds work rationally whenever they see something as obvious! If this is true, it is an empirical fact; and you should be able to see the alternative as possible!”
Indeed, 2+2=4 is only true in some contexts. For example, sometimes 1+1=1 -- in contexts where separate objects lose their distinct identity as soon as they are grouped. (Think of a particular object several times. How many times did you think of it? But how many objects did you think of?)
Later edit: It is interesting that such a benign comment would get 4 down votes. Perhaps I understand this group well enough to guess why: the experiment I suggested is an entirely “internal” one, it provides no external proof of what I am suggesting. I think that a common reader here feels dismissive of, if not entirely antagonistically towards, knowledge that is internally generated. Personally, I have a preference for the knowledge that arises from internal experience.
I agree that the downvoting of this comment was overly harsh. My theory on why it occurred is different, and best illustrated by an example: if someone posted a comment saying “2+2=4 is only true in some contexts; in arithmetic modulo 3, 2+2=1”, that comment would have been similarly downvoted.
However, let me be so bold as to say a word in defense of even that hypothetical commenter. Anyone mathematically sophisticated (including our downvoters) will agree that it is possible to construct a mathematical system in which 2+2 equals anything you like—or, more precisely, for any symbol x, a system can be constructed in which the formula (string of symbols) “2+2 = x” is given the label “TRUE”. Mod 3 arithmetic is an example for x = “1”.
Now, it is at this point that the downvoters protest: “But this is not the same thing as saying 2+2=1! All you’ve done is change the meaning of the symbols in the formula, such as ‘2’ and ‘1’. Two plus two is still four, for the original meaning of those words. You’re confusing the map and the territory. Downvoted!”
Well, the downvoters do have a point. But, at the same time, let me suggest that they’re also making the same mistake as our poor beleaguered commenter!
What they’ve done, you see, is to make a leap from “Ordinary (i.e. non mod-3, etc.) Arithmetic accurately models certain physical phenomena” to something like “Ordinary Arithmetic is true in (or of) the physical world”. Instead of saying what they mean, which is “the physical world is best modeled by a system that has ‘2+2=4’ as a ‘TRUE’ formula”, they say “2+2 is in fact equal to 4″.
Small wonder that confusion arises about whether mathematical statements are “emprical” or not! “The physical world is best modeled by a system that has ‘2+2=4’ as a ‘TRUE’ formula” is clearly an empirical claim. But what about 2+2 = 4, all by itself? When a mathematician at a blackboard proves that 2+2=4 in Ordinary Arithmetic (or, for Eliezer’s benefit, that infinite sets exist in standard set theory), has he or she made a claim about physics? No! Not without the additional assumption that the formal system being used is in fact an accurate map of the territory! But the mathematician makes no such assumption; he or she (acting as a mathematician) is interested only in the properties of formal systems. (Yes, that’s right: I’m advocating the view known as formalism here. The other well-known positions in the philosophy of mathematics, namely Platonism and intuitionism, suffer from map-territory confusion!)
Mathematical systems, like Ordinary Arithmetic or Mod-3 Arithmetic, are part of the map, not the territory. The facts of mathematics are, so to speak, cartographic, rather than geographic.
In the OB post tautologies have to be empirically observed somehow, Eliezer writes about waking up one day and discovering all sorts of evidence that 2+2=3. This wouldn’t be evidence that 2+2=3 in Peano arithmetic, it would be evidence that Peano arithmetic just doesn’t apply for some reason. In my down-voted comment, I was just giving an example of how there can be different kinds of arithmetic if you are willing to be flexible about what arithmetic is. (If you are not willing to be flexible, then you are not willing to allow the observation that 2+2=3 as an observation about arithmetic, because this is not possibly true in standard arithmetic. Well, the observations are possible but you’d have to account for it as some kind of grand delusion.) My point is that 2+2=4 in Peano Arithmetic independent of observation, but observation tells you if Peano arithmetic applies or not.
Exactly.
It is worth emphasizing that to claim that “2+2=4 in Peano Arithmetic independent of observation” is not to claim that our knowledge of this fact about Peano Arithmetic is independent of observation. (The former claim is about our map of the territory; the latter is about our map of our map of the territory.)
Could you elaborate? It sounds to me like the former claim is about the territory, and the latter is just hard for me to parse.
I’ll emphasize with the following analogy: you need to observe the sun to know of it. However, you can nevertheless be certain—as certain as you are of anything at all—that the sun exists independently of observation. You need to define the Peano axioms and observe the deductions that lead to the tautologies to know of them, but they are mathematically true independent of your observation.
How many words are in this list?
Duck
Duck
Goose
The list contains 3 word instances and represents 2 word prototypes.
The jargon I was looking for was 3 tokens of 2 types, but close enough :)
Heh, with the right jargon, you can accomplish anything. ;)
Doesn’t that just mean that grouping doesn’t always correspond to addition?
Yes. If 1+1 is anything other than 2, then it’s not addition. I gave an example of how combining two things together doesn’t always yield addition.
Saying that 2+2=4 is a tautology in a certain axiomatic system defined with ‘+’ means that you couldn’t have anything but 2+2=4 in that system. It’s simply mandatory, and a rational person could not wake up one day and be convinced that 2+2=3 within a self-consistent system that deduces 2+2=4.
While tautological truth is independent of observation (let’s call it mathematical truth), it is dependent upon context (i.e., a self-consistent axiomatic system). Some mathematical truths in one axiomatic system are false in another. When we talk about whether a a mathematical statement is true, we need to specify the context, and, in my opinion, in the most demanding definition of truth, the context is the real, actual, empirical world. So I agree with Eliezer that a mathematical tautology must be observed in order to be true.
When we humans talk about “2+2=4”, it is because we have chosen arithmetic from an infinite number of possible axiomatic systems and given it a name and a set of agreed-upon symbols. Why did we do that? Because we observed arithmetic empirically. Obviously, addition is just one operation of infinitely many operations. The ones we have defined (multiplication, subtraction, addition mod n, taking the cardinality of subsets of, etc.) usually have some empirical relevance. While we don’t feel very comfortable thinking of those that don’t (and this says somethng about the way we think), I have faith that if we were presented with a very strange set of observations, it would take a pretty short amount of time to train ourselves to think of the new operation as a “natural” one.
… I idly wonder if there is a such thing as a mathematical truth that could not be realized empirically, in any context, and if there would be any way of deducing it’s non-feasability.
Is saying “we could have a different axiomatic system” different from saying “2, 4, +, and = could all mean different things? Of course we’ve only defined the operations and terms that are useful to us. I don’t care about the naturalness of ‘+’ only that once I know the meaning of the operations and terms the answer is obvious and indisputable.
Math isn’t my field, so my all means show me how I’m wrong.