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.

... this "perfomative contradition" doesn't refute their argument. — Michael

Nice ... On that point, I yield. :sad:

The epistemological solipsist says that one cannot know that there are other minds, — Michael

Who is this one ? Is this not the issue ? Is he saying that he cannot know ? Or that 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 ?

Given the context, I think the last option makes most sense. But both of the last two seem problematic, with the first being irrelevant.

:clap:

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.

He's saying that knowledge of other minds is impossible. — Michael

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

.

The solipsist can argue as if there are other minds, and still claim that he doesn't know that there are other minds. — Michael

The problem is when the solipsist tells me that I can't know there's a world beyond me.

I think we are neglecting the 'external world' theme, which I see as just important.

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.)

It's different in that it doesn't make such a claim? — Michael

I mean why pick it out? Do we have epistemological hat-denial, where I make the claim that we can't have knowledge of hats?

'Other minds' has been picked out as 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.

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.

'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.

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.

:up:

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.

It just claims that knowledge of other minds is impossible. — Michael

So it claims that I can't know there are other minds ?

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

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

How do you take external ? We don't want to be too specific, in my view. One need not have a settled metaphysical view on the nature of our world (that it's really X or actually Y).

and if there are other minds then these other minds cannot know that there are other minds. — Michael

Normative of psychological claim ? And isn't this a claim about something beyond him ? The world is such that, if there are other rational minds, then those minds will have a nature such that ....(or be bound to rational norms such that ...)

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. This claim seems to transcend the claimant, seems to be aimed beyond his experience.

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.

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. — Michael

My post wasn't really about what the solipsist can claim. I mean, I can claim to be the king of Spain.

We're engaged in philosophy here and like any other game, there has to be rules of engagement. Otherwise we're just writing unconnected posts at each other, which seems pointless.

So, although vague, we examine claims made in this game using rules like 'coherence', 'consistency', etc.

The point is that the reasons the solipsist uses to argue against other minds apply to those other claims equally, so they cannot make those claims and remain consistent, which is (vaguely) one of the rules.

Of course they can make them anyway, but they'll just no longer be playing the game of 'making a rational argument', they'll be playing some other game.

It doesn't make sense — Pie

It doesn't make sense — Pie

Yep, it doth not make any sense at all!

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). — Michael

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 normative (?) claims about him which are himself ?

In case it helps, I don't think 'material' is easy to cash. I intentionally generalize 'external' to 'something I can be wrong about' to minimize my presuppositions and maximize the generality of my conclusions.

Consider the thread's theme, our minimal epistemic commitment. We can argue endlessly about the nature of the 'space' we share, about the meaning of 'material' and 'mental,' but it doesn't make sense to say we can't be right or wrong, for that is to say that it's wrong to think we can be wrong.

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

The point is that it's a claim about norms, about constraints on possible rational agents. It's a thesis about the world, that it contains such norms.

The only thing that matters to this discussion is the truth or falsity of the proposition "knowledge of other minds is impossible". — Michael

To me the issue is just as much about an 'external' world.

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

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

And, again, nobody is making such a claim.

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 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.

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

I know...so what do you make of external world ? How do you cash that out ? It's 'outside' the self, different from the self.

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). — Michael

In what sense, then, are they external ?

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

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 $\sqrt{2}$ 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.

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.

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

I basically agree, and it seems to be a truth about something external to our epistemological solipsist, for it doesn't die with him or need him around. And "we can't know there's a world" seems to be about the world in the same way.

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. — Michael

This is problematic. You are retreating into figurative uses (putting them in quotes ) of the words I'm asking you to clarify in the first place. Independent of the subject might as well be 'external,' unless the spatial metaphor is important.

Not everyone says that atoms are "external." Consider Mach's weird views, which are adjacent to solipsism. Platonism is widely challenged. The main point is that those setting beliefs together rationally understand that they can be right or wrong.