The 'we' is 'deeper' or more 'primordial' than the (linguistic) 'I.' — Pie

I doubt that. If we look to non-human animals, and perhaps babies and people with certain developmental disabilities like autism, I suspect that they have a greater difficulty in understanding that other animals/people have minds and thoughts and feelings like their own. The notion of "other minds" requires a degree of inference that comes after self-recognition. To understand that other people have minds you must first understand that you have a mind.

You can share an understanding and not know that you share an understanding. And at least on the non-solipsist's end he must admit to a known shared understanding. So it would be hypocritical of the non-solipsist to demand of the solipsist what he won't demand of himself.

If the non-solipsist claims that other minds and mind-independent objects can be known to exist and the solipsist claims that they can’t be known to exist, and if they accept that their positions are incompatible, then they accept that there is some shared understanding of what it means to exist, whatever that is.

So as I said, if you think that the meaning of “exists” first needs to be explained then you must be quiet on the debate between solipsism and non-solipsism.

But it seems to me that you want the solipsist to explain what it means to exist whilst simultaneously claiming that other minds and mind-independent objects can be known to exist, which is clearly special pleading.

The key part is that it’s about what exists. We can be wrong about maths and trees, but unlike mathematical entities (at least according to the antirealist), trees are thought to exist. It’s independent existence that solipsists claim cannot be known.

As for what it means for something to exist, presumably it means what it means when the non-solipsist claims that mind-independent objects and other minds can be known to exist.

If you think the very notion of existence isn’t clear then I don’t think you can claim that other minds exist and so you must be quiet on the matter.

ES makes the claim about our shared situation that we should not assume we are in a shared situation. — Pie

Again, it doesn’t say that we shouldn’t assume that there are other minds. It says that we cannot know that there are other minds.

If you accept that we can only ever assume that there are other minds then you accept the solipsist’s skepticism.

But claiming that X doesn't exist is a claim about something, about our 'external' 'world.' — Pie

It’s a claim about X. I don’t understand this external world concept of yours. It doesn’t seem to be anything like what is usually meant, which concerns the existence of objects that are independent of my mind. That’s the kind of external world that solipsism says cannot be known.

As I keep saying, we can make claims about things that don’t exist, and about things that do exist but that cannot be known to exist. Your arguments just don’t seem to address the claim being made by solipsists, which is just about the limitations of knowledge.

I don’t know what you mean by asking who it’s true for. It’s just either true or false. And then, as a separate matter, there may exist one or more conscious entities.

Independent of the subject might as well be 'external,' — Pie

I think there’s a difference between saying that something has an independent existence and saying that the truth of something is independent of what I say or believe. A mathematical antirealist will reject the independent existence of mathematical entities but can accept that we can get maths wrong.

The solipsist argues that we cannot know that anything exists independently. He doesn’t argue that claims don’t have a truth-value. In fact, the solipsist can accept that “there is a material world and there are other minds” is true; he just argues that it cannot be known to be true.

We don't need Platonism. That would be one of those claims that could be right or wrong. It suffices to see that math is normative, that a proof that √2 is irrational is also a proof that all mathematicians as such ought to regard it as such, recognizing a fact about the real number system, independent of any metaphysical theory of something 'behind' this system. — Pie

And root 2 is irrational even if I’m the only man alive. It’s even irrational even if nobody is alive.

In what sense, then, are they external ? — Pie

I don’t think “external” is the right word. It’s “independent” in the sense that we can be wrong when we do maths, but mathematical entities don’t have some “external” existence in the way that atoms or Platonic ideas are said to have. It is this “external” existence that solipsism denies. It doesn’t deny truth-aptness.

But it starts to get a bit silly, for now we have a subject who 'is' all of mathematics, and the epistemological solipsist is therefore only making claims about him which are himself ? — Pie

That's a false dichotomy. It's not a case of either a) mathematical realism is true or b) I am maths.

ES says : It's wrong to assume there is something we can be wrong about. — Pie

Not it doesn't. It says that knowledge of other minds (and an external world) is impossible.

but it doesn't make sense to say we can't be right or wrong — Pie

And, again, nobody is making such a claim.

I take 'external' to be something or anything other than the subject. — Pie

Maths and logic are something "other" than the subject, but I don't think it right to think of them as being "external" (in the sense that the material world is said to be external).

And isn't this a claim about something beyond him ? The world is such that, if there are other rational minds, then ....

We can make claims about things that don't exist. p → q is true even if p is false.

For me the issue is that the claimant wants to bind or makes a normative claim on all possible rational agents, the rational agent as such.

The only thing that matters to this discussion is the truth or falsity of the proposition "knowledge of other minds is impossible". Forget the solipsist and his actions. They're irrelevant. You can't argue against the claim that it is wrong to kill by pointing out that the person who made the claim is a murderer.

He's saying that knowledge of other minds is impossible. Therefore, he cannot know that there are other minds, and if there are other minds then these other minds cannot know that there are other minds. — Michael

ES claims that it's irrational to assume that one can be irrational, wrong to assume there's something one can be wrong about (an 'external world' as a target of claims.) — Pie

It doesn't. It just claims that knowledge of other minds is impossible. I honestly don't know how you keep inferring the above from that.

The "external world" as you mean here isn't what the solipsist (or idealist) means.

To which the counter argument would be that you've misunderstood the meaning of the word 'knowledge', since we use it quite felicitously on a daily basis. — Isaac

Well, not everybody buys into such a Wittgensteinian interpretation of language. Many philosophers think that there is some greater substance to the meaning of such words as "knowledge", "truth", "good", "other minds", etc. than just conventional use.

'Other minds' has been picked out ss a thing we can't have knowledge of, but the case you're presenting just seems to be a generic case against knowledge of any sort. — Isaac

Not really. The solipsist can claim to know that he exists, that he is happy, that he sees a tree, that the square root of four is two, that modus ponens is a valid rule of inference, and that knowledge of other minds is impossible.

How is this any different to saying that knowledge of anything is impossible? — Isaac

It's different in that it doesn't make such a claim? I don't understand your question. If I claim that knowledge of the distant future is impossible am I saying that knowledge of anything is impossible?

Who is this one ? Is he saying that he cannot know ? Or that's it's the nature (psychological) of other minds that they can't know ? Or that it's irrational or unjustified (normative rationality) for such an other mind to claim to know ? — Pie

He's saying that knowledge of other minds is impossible. Therefore, he cannot know that there are other minds, and if there are other minds then these other minds cannot know that there are other minds.

Non sequitur; I neither claimed nor implied as much. Your / solipsist's reliance on logic, however, presupposes others. Read what I actually wrote again. — 180 Proof

This is a non sequitur. Even if the solipsist's "reliance" on logic presupposes others (which you have yet to explain), this "perfomative contradition" doesn't refute their argument. I live as if I won't die tomorrow, but I don't know that I won't die tomorrow. The solipsist can argue as if there are other minds, and still claim that he doesn't know that there are other minds.

As I've pointed out, your argument doesn't even do that. — 180 Proof

So you think that it's incoherent for a single mind to be the last survivor? Either everybody dies or at least two don't? Or conversely, when the first mind(s) came into being, you think it incoherent to suggest that the first mind was alone? It must have at least been a pair?

These seem like unreasonable claims. If the number of minds is finite then some cardinal number n is the number of minds. I don't see why it would be coherent for n to be 2 but incoherent for n to be 1.

My primary point is that epistemological solipsism is incoherent as a claim about other minds in general, namely that they ought not just assume that such other minds exist. — Pie

The epistemological solipsist says that one cannot know that there are other minds, he doesn't say anything about what one should or should not assume.

I can't know that I won't die tomorrow, but I'm going to assume and live as if I won't.

In fact, assumptions entail skepticism. If I knew something then it wouldn't be an assumption.

Without all of the premises being true, your argument is not a sound one, sir. — 180 Proof

It's not supposed to be a sound argument. It's supposed to show that the claim "only one mind exists" is coherent.

And, as pointed out, even (your) reliance on logic – normative rationality – presupposes selves-other-than-yourself — 180 Proof

I don't understand this. Classical logic (and others) doesn't depend on there being other people. Even if I'm the last (or first) man alive, the various axioms and rules of inference hold. The law of noncontradiction doesn't just fade away in a nuclear holocaust where I'm the only survivor.

But then it's just a contingent fact that other minds don't exist. We're not in the original situation of worrying about apparent minds that might be p-zombie or fantasies. — Pie

Regardless of what brings about the situation where only one mind exists (it could be that there were other minds but they died, or it could be that only one mind ever came into being), the claim that just one mind exists (or that only one mind can be known to exist) is coherent, contrary to your objection.

I'm guessing that some people imagine the solipsist as living in a world like ours that 'may' be just his fantasy... — Pie

I don't know why you think it would be a fantasy. Experiences are real, not made up.

... and they imagine him (problematically, in my view ) being able to make claims that are wrong or right about this fantasy world.

I think this may be part of where you're going wrong. I can talk about things that don't exist. Even if atheism is true I can talk about God, and if I claim that God exists then my claim is false. Even if solipsism is true I can talk about an external material world, and if I claim that such an external material world exists then my claim is false. Even if solipsism is true I can talk about other minds, and if I claim that other minds exist then my claim is false.

I can also make true or false claims about my experiences. I can feel pain and yet claim not to feel pain. So even claims about my "fantasy" world are truth-apt.

I’ll make another argument. It is possible that the number of minds is finite and it is possible that every mind is mortal. It is possible that every mind except one dies. Therefore it is possible that only one mind exists. Nothing about this scenario is incoherent, therefore the solipsist’s claim that only one mind exists is coherent. The coherency of the conclusion doesn’t depend on any of the premises being (or having been) true.

To me that's a misleading analogy. If I claim there is a God, I'm saying that for both us there is a God. It's a fact about our world in common that there's a God in it.

If I say, on the other hand, that it's a fact about our world together that we might not have a world together, that's different. — Pie

You seem to be saying that if p → q is true then p is true, but that's an invalid inference. p → q is true even if p is false. In this case, p is "there are other minds" and q is "these other minds cannot know that there are other minds".

We can try to repair this: "If there are other minds, then those minds can't know there are other minds." But this is a statement about the very minds that might not exist. — Pie

And? If there is the Christian God then he is a dick. The statement is about the very God that might not exist. What's the problem? The existence of something is not entailed by there being some true claim about it.

Edit: In fact, I think it can be correct to say that the Christian God is a dick even if he doesn't exist, and so it can be correct to say that others minds cannot know that there are other minds even if they don't exist.

Consider though : their claim is about other minds. Other minds can't know whether there are other minds. The keyword is we. — Pie

Yes. What's wrong with that? Just as there can be an agnostic theist there can be an epistemological solipsist who isn't an ontological solipsist. They just accept that we cannot know that there are other minds, but nonetheless believe that there are.

I'm trying to dig to the gist of the appearance / reality distinction, which seems tied in to the concept of the self. — Pie

Then I think you're drawing an invalid conclusion and so your reductio ad absurdum is a non sequitur, because nothing about saying that only one's mind and mental phenomena exists entails that no claims are truth-apt.

So epistemological solipsists say that we might be wrong to think that we could be wrong ? We can't be sure about whether there's something we can be wrong about. — Pie

I don't know what you mean here. They just claim that we can't know that there are other minds, just as agnostics claim that we can't know whether or not God exists, and I claim that we can't know what will happen in the distant future.

It's a free, satirical translation of solipsism. — Pie

Solipsists don't make such a claim though. Epistemological solipsists only say that we can't know that there are other minds and ontological solipsists say that "there are other minds" is false.

This one. "There's nothing that we can be right or wrong about." — Pie

Who makes such a claim?

But if 'external world' means "that which we can be wrong or right about," it's incoherent to reject or doubt it. — Pie

Given that the solipsist says that solipsism is right and non-solipsism wrong, and that the idealist says that idealism is right and materialism/dualism wrong, and that the anti-realist says that anti-realism is right and realism wrong, this clearly isn't what any of these positions mean by "external world".

But also your claim above is ambiguous. Which of these are you saying is incoherent?

1. "there's nothing that we can be right or wrong about"
2. "none of the things that we can be right or wrong about exist"

t seems to me that everything is up for debate except for there to be something that's up for debate. — Pie

Yes. And that something can be the existence of other minds, or an external material world, or God, or the soul, or mind-independent mathematical entities.

So, again, I don't really understand what you're trying to say here.

Yes.

What is the claim about ? An otherwise radically unspecified world. — Pie

It's about what does or doesn't exist, and the nature of what exists.

What is the difference between reckless assertion and an argument ? Conforming to a logic that binds or ought to bind all rational minds. — Pie

Which logic? Classical? Free? Paraconsistent?

Regardless, I'm not sure what this has to do with either solipsism or idealism. Neither of these positions are anti-logic.

I don't know, perhaps you could tell me.

The solipsist will say that the world is one's own mind (or for the epistemic solipsist, that one's own mind is the only worldly thing that can be known), and the idealist will say that the world is immaterial. So I'm still not entirely sure what you're trying to say.

I point out that any attempt to deny it assumes what it would deny. — Pie

I'm not quite sure what you mean by this. Are you saying that solipsism assumes other minds, that idealism assumes an external material world, that eliminative materialism assumes mental states, etc.?

You also seem to misunderstand Dummett. He doesn't say that every true statement must be recognized as true, he says that every true statement must be recognizable as true. The cat having fur (or not) is recognizable even if not recognized.

But that aside, the point I was making to Pie is that if he is to be consistent with his reasoning then he must accept that it is public norms that determine the meaning and proper use of the words "true" and "false" which is incompatible with realism which argues that the truth is not determined by our linguistic (or other) conventions.

Dummet wants to have a level of "true" and "false" outside of language — Banno

No he doesn't, that's the point. The principle of bivalence, however, requires that it is, as that is the only way that every statement can be determinately true or false.

creativesoul misunderstands and doesn't address the argument being made. Read the quote in the opening post.