OK, let's be completely, utterly, crystal clear about this.
1. I observe that people who do not base their actions on sensory experience do stupid things.
2. Therefore, true knowledge or justification comes primarily from sensory experience and empirical evidence.
You're telling me that 2 is a logical implication of 1? You're perfectly happy with the way I've framed this---there are no hidden premises or anything like that? 2 is a direct, logical implication of 1?
I am not "perfectly happy" with it, no. For starters, I don't think there actually are people who do not base their actions on sensory experiences. Evolution mitigates against that pretty strongly.
I would say that if someone doesn't base their actions on sensory experience (a very big if) then they will be totally unable to navigate reality. They will almost certainly injure themselves, possibly others, and likely even kill themselves and maybe take others down with them. It's so obvious and the consequences so severe that it would be unethical to actually conduct this experiment.
Also, 2 is not a logical implication of 1. One can never rule out the possibility that, say, all human behavior is controlled by evil demons. What I would say is that my version of 1 is very compelling evidence for 2, and one of the things that makes it compelling is that it is so obviously true that a sane person would never even contemplate it as anything other than a thought experiment.
BTW, would you have any interest in being a guest on a podcast?
>Also, 2 is not a logical implication of 1. One can never rule out the possibility that, say, all human behavior is controlled by evil demons. What I would say is that my version of 1 is very compelling evidence for 2, and one of the things that makes it compelling is that it is so obviously true that a sane person would never even contemplate it as anything other than a thought experiment.
Oh good, ok - you see my confusion, I thought you were saying that it was a logical implication. I would still say that 2 isn't really grounded in 1 so much as it is self-evidently true. Like, if we're being controlled by evil demons, 1 isn't even relevant---the question is fundamentally whether sense-experience gives us true knowledge bar extenuating circumstances or not; I think the answer is yes, but not because we see that this belief is a useful belief, it's because 2 itself is intuitively true. I don't believe that my perception of me sitting on a chair is good grounds for the proposition that I really am sitting on a chair not because of a thought experiment about lacking that belief leading to injury---I believe it because it seems true itself. And I think this is the right solution in general for related issues, whether it's inductive inferences (I think they're rational), belief in causality, belief in the validity of sense-data, or any other typical issue for empiricism.
The "X is key for survival, so X must be true" way of thinking has never been appealing to me---this seems to miss the point of what it means for something to be true. Like, I don't believe in 1+1=2 because it's useful for economics, physics, math, or whatever---I think it's true independently of its utility. Similarly for other truths.
>podcast
I'd prefer to not publicize my real name and face, so no, unfortunately (unless you'd be OK with that; I'd be happy to chat if so).
> I don't believe in 1+1=2 because it's useful for economics, physics, math, or whatever---I think it's true independently of its utility.
I actually doubt that. What do you think 11+27 is? If your answer was "38" then the followup question is: suppose it is 11:00. What time will it be 27 hours from now?
The "correct" answer to "what is 11+27" depends on circumstances in the real world (and so does 1+1). There are no Platonic truths, only preferred models.
> X is key for survival, so X must be true
It's not that. It's "X is a faithful reflection of the actual state of affairs in objective reality." That's what the word "true" means.
It just so happens that the actual state of affairs in objective reality has an impact on survival, so having a faithful reflection of it in your brain is handy. That's the reason "truth" is a thing.
> I'd prefer to not publicize my real name and face
Well, a podcast is voice only, so that's not really a show-stopper.
>There are no Platonic truths, only preferred models.
Yeah, I disagree, I think there's something mathematical truths reflect that are independent of the physical world. When we decide whether certain mathematical claims are true or not, say, Fermat's last theorem---we prove them mathematically, we don't want to appeal to their utility or lack thereof, right? My reasoning for not wanting to appeal to utility for the validity of sense-data is analogous.
>That's what the word "true" means.
I agree.
>It just so happens that the actual state of affairs in objective reality has an impact on survival, so having a faithful reflection of it in your brain is handy.
I agree.
>That's the reason "truth" is a thing.
Well, truth is a thing regardless of whether or not we evolved to be able to hold such a concept in our minds, no?
> When we decide whether certain mathematical claims are true or not, say, Fermat's last theorem---we prove them mathematically, we don't want to appeal to their utility or lack thereof, right?
Well, sort of. We don't care about the utility of Fermat's last theorem per se, but the only reason we care about numbers, which is what Fermat's last theorem is about, is because numbers have utility. It turns out that, having invented numbers for their utility, they also make fun mental playthings. But they were invented to keep track of how many sheep you had.
> Well, truth is a thing regardless of whether or not we evolved to be able to hold such a concept in our minds, no?
No. Truth is a property of propositions, so it only makes sense to talk about truth in the context of something that can harbor a proposition. If such a thing does not exist then neither do propositions and hence neither does truth. It's kind of like talking about "the mass of an idea". Mass is a property of matter, so it doesn't make sense to apply it to something that isn't made of matter.
The thing that encodes propositions doesn't have to be a human brain, of course. It could be an alien brain, or a computer, perhaps even a thermostat (that one is debatable). But it has to be something.
All that's fine---but I think you would agree that Fermat's last theorem isn't true by virtue of its utility for counting sheep or anything like that. Similarly, I don't think that the fact the physical world exists in the manner suggested by sense-data is true by virtue of its utility for preventing us from dying.
>The thing that encodes propositions doesn't have to be a human brain, of course. It could be an alien brain, or a computer, perhaps even a thermostat (that one is debatable). But it has to be something.
Are you saying that if there were no humans (or anything capable of encoding propositions) to conceive of it, the proposition "the earth is round" wouldn't be true---in other words, it would not be true that the earth is round? That seems to defy common sense.
> I think you would agree that Fermat's last theorem isn't true by virtue of its utility for counting sheep or anything like that. Similarly, I don't think that the fact the physical world exists in the manner suggested by sense-data is true by virtue of its utility for preventing us from dying.
I actually would not agree with either of those.
> Are you saying that if there were no humans (or anything capable of encoding propositions) to conceive of it, the proposition "the earth is round" wouldn't be true---in other words, it would not be true that the earth is round? That seems to defy common sense.
Yes, I get that. This is not an easy concept to wrap your brain around, and I totally understand if you think it sounds like I'm absolutely crazy. But nonetheless, it is the case that if there were no humans (or anything capable of encoding propositions) to conceive of it, the proposition "the earth is round" would not be true. The reason is that if there were nothing capable of encoding that proposition, that proposition could not exist. A non-existent thing cannot have any properties, and so a non-existent proposition cannot be true.
Two important things to note: first, the proposition "the earth is round" would not be true in a world where there is nothing capable of encoding propositions, but neither would it be false. It would simply be non-existent. And second, despite the fact that the proposition "the earth is round" would be neither true nor false, the earth would still be round. But we can only make that observation because we live in a world where there are things capable of encoding propositions. It's really hard to imagine a world where that is not the case because we would not exist in such a world.
Here is a thought experiment that might help: consider some proposition P that has never been conceived of and will never be conceived of by anything capable of encoding propositions. Such propositions must exist because there are an infinite number of propositions but we live in a finite universe, and so only a finite number of propositions can ever be encoded. In fact, there must be an infinite number of such propositions. Are those propositions true or are they false?
>It's "X is a faithful reflection of the actual state of affairs in objective reality." That's what the word "true" means.
As you've said earlier. This sounds like a reasonable construal of the word true. But I don't see anything about propositions needing to be encoded in this definition. "The earth is round" is a faithful reflection of the actual state of affairs in objective reality. It was a faithful reflection of the actual state of affairs in objective reality even before anyone was around to conceptualize this as a proposition. You don't think so?
Propositions are ideas, i.e. they exist in a different ontological category than material objects like earth (note no quotation marks). The word "earth" (with quotes) is an idea, one that happens to refer to earth, i.e. the material object referred to by the word "earth", which happens to be round. The words "earth is round" (with quotes) is also an idea, one which refers to a particular property (roundness) of a particular material object (earth). That idea falls into a subset of the more general concept of ideas which we call "propositions" because they have a particular relationship to the states of material objects, i.e. "the earth is round" (with quotes) is true because the earth is round (no quotes).
Material objects are made of atoms; they cannot exist without the atoms that comprise them, but their existence is more than just the totality of the existence of their constituent atoms. All of the atoms that comprise the earth existed billions of years before the earth came into existence. Earth did not come into existence until the atoms that comprise it arranged themselves in a particular way.
Ideas are not made of atoms, they are made of information. Just like material objects, ideas do not come into existence until some information that encodes that idea arranges itself in a particular way, i.e. until they are thought of. A proposition that hasn't been thought of is like a poem that hasn't been written. Saying that an unthought-of proposition is true is like saying that an unwritten poem rhymes.
Consider the words "Darth Vader was Luke Skywalker's father." Do those words stand for a proposition? Is that proposition true? Was it true before 1977 (keeping in mind here that the Star Wars story ostensibly happened "a long time ago")? Would Rene Descartes be able to recognize it as a true proposition?
It's really hard to talk about ideas. With material object you can point at them, poke them, prod them, weight them, shine lights at them. You can't do any of those things with ideas. All you can do is refer to them using representations like "the earth is round" (with quotes) or "la terre est ronde" or "Die Erde ist rund" or "地球是圆的". It is the act of referring to them in a way that some being can recognize as referring to a proposition that causes the proposition to come into being, just as the act of composing a poem causes that poem to come into being. Unwritten poems do not rhyme, and they do not not-rhyme. They simply aren't. Likewise, unthought-of propositions are neither true nor false.
Here's what I understand you to be saying, and you're free to reframe this.
1. Propositions are ideas.
2. Ideas can only exist if they are conceived.
3. "The earth is round" is a proposition.
4. Therefore, "the earth is round" can only exist if it is conceived.
5. Truth and falsity are properties of propositions.
6. If something does not exist, it cannot have any properties.
6. If it is not conceived, "the earth is round" cannot exist.
7. "The earth is round" cannot have any properties.
8. Truth and falsity are not properties of "the earth is round".
Sounds reasonable. But how do we square this with:
1. "The earth is round" reflects a state of affairs about objective reality.
2. If something reflects a state of affairs about objective reality, it is true.
3. "The earth is round" is true.
There's nothing here about "the earth is round" needing to be conceived by someone.
One issue I would raise is the first argument's 1 and 2. Propositions don't just exist insofar as they are conceived. Representations of propositions, sure, but not propositions themselves.
> There's nothing here about "the earth is round" needing to be conceived by someone.
Yes, there is. You can't talk about a proposition without conceiving of it. The instant you wrote “"The earth is round"” (note the nested quotes) you conceived of the proposition "the earth is round" and brought it into being. This is impossible to avoid. So this:
> There's nothing here about "the earth is round" needing to be conceived by someone.
is false.
> Propositions don't just exist insofar as they are conceived. Representations of propositions, sure, but not propositions themselves.
I already gave you the answer to this in the parent comment but you ignored it.
"Ideas are not made of atoms, they are made of information. Just like material objects, ideas do not come into existence until some information that encodes that idea arranges itself in a particular way, i.e. until they are thought of."
etc.
So that is (still) my answer: you are simply mistaken when you say that "Propositions don't just exist insofar as they are conceived."
(You're in good company. Plato got this wrong too, and he was no dummy. But he didn't have Alan Turing's shoulders to stand on.)
BTW, note that the converse is not true. You can conceive of an idea without rendering it into a representation. Indeed, you can conceive of an idea without even being able to render it into a representation. (This is actually quite common!) But what you can't do is produce a rendering of an idea into a representation without conceiving of the idea being represented. (BTW, that is not quite true. There is a tiny loophole, but I'm going to leave it as an exercise for you to figure out what it is.)
In the second argument, could you tell me which of (1) and (2) are incorrect, and why?
If it's the quotes that are problematic, I'm fine to drop those.
The earth is round, regardless of whether people have this idea in their heads or not. You deny this?
>I already gave you the answer to this in the parent comment but you ignored it.
But I didn't disagree that ideas are not made of atoms. What I disagreed with is that propositions only exist insofar as they are conceived.
>(You're in good company. Plato got this wrong too, and he was no dummy. But he didn't have Alan Turing's shoulders to stand on.)
What did Turing do that proved that propositions only exist insofar as they are conceived? Or are you just talking about scientific progress in general?
> The earth is round, regardless of whether people have this idea in their heads or not. You deny this?
No. What I deny is that "the earth is round" and "the proposition 'the earth is round' is true" are identical propositions. The first is a proposition that makes a claim about the roundness of the earth, and the second is a proposition that makes a claim about the truth of a proposition. Those aren't the same thing.
The earth is round whether or not anyone is around to contemplate it (the earth). But "the earth is round" is not true unless someone is around to contemplate it (the proposition).
> What did Turing do that proved that propositions only exist insofar as they are conceived?
That's a long story, and I have to run to a meeting right now. If you really want to know, remind me later. I may need to write a blog post about it.
But forget about propositions for the moment. Do you think that unwritten poems exist?
So, I think if saying "the earth is round" is true and saying the earth is round mean different things, then we haven't construed the former properly, the former should be construed as expressing the same thing as the latter. If it's just a linguistic disagreement, then I think we can set that aside, I'm not very interested in that. The original point was that we can intuit certain things as being true, e.g. that sense-data reflects something about reality, and there's no need to appeal to how useful believing this is or isn't. Like, conceivably, nuclear wars could lead to the annihilation of humanity, but I don't see why that should have any bearing on whether atomic bombs exist or not.
> the former should be construed as expressing the same thing as the latter. If it's just a linguistic disagreement, then I think we can set that aside
No, this is not just a linguistic disagreement. This is the crux of the matter. By saying that "the earth is round" and "the proposition 'the earth is round' is true" mean the same thing you are conflating two different ontological categories. When you do that, your reasoning is no longer sound.
Consider this:
P1: The U.S.S. Enterprise can travel faster than light.
Is P1 true? If yes, then how can that be when we know from relativity theory that nothing can travel faster than light? And if no, then what about these:
P2: The U.S.S. Enterprise is powered by a matter-anti-matter reaction controlled by dilithium crystals.
P3: The U.S.S. Enterprise is powered by squirrels running on treadmills.
---
P.S. It occurred to me that there is a TL;DR answer to the question of what Turing did that was so important: he invented general-purpose software.
