Even if X is a property of something that exists in my mind it doesn't follow that I know that it will cause Y. You're just asserting that the solipsist will have knowledge of the future without explaining how you came to that conclusion. — Michael

Nope, I explained my reasoning for that conclusion a while back too, but it too went by unremarked on.

If all that exists is one's mind, and if this is asserted or entertained on the grounds of scepticism of indirect inference, then there cannot be any hidden states in the mind. That means that the full properties of any entity must be known. 'All things it will cause' is a property of an entity.

it isn't a given that ontological solipsism entails hard determinism. It could be that probabilities/randomness is involved in mental phenomena. — Michael

It is, because, as above, if a part of the mind is not presented directly to our awareness (there's a source of uncertainty, then that source must (consistently) be doubted in the same way as the external world is. If some aspects of my world seem random I'm not directly aware of the forces involved, therefore I must doubt the existence fo the forces involved.

Same with this. It doesn't follow from X being a property of something that exists in my mind that I know that it cannot lead to Y. — Michael

It follows from all possible causes of all possible events being in your mind.

You don't find the decimal notation of pi, or the truth of the Reimann hypothesis, written onto atoms or whatever, or on sense data, and mathematical realism is false. — Michael

Whether mathematical realism is false is another discussion, I put in all the possible explanations for any given approach to mathematics.

They'd be wrong.

1. John knows that Joe Biden is President
2. Joe Biden is 79 years old
3. Therefore, John knows that Joe Biden is 79 years old

Obviously the conclusion doesn't follow. The same with:

1. John knows that X, Y, and Z exist
2. Only X, Y, and Z exist
3. Therefore, John knows that only X, Y, and Z exist

The conclusion doesn't follow. — Michael

Of course it doesn't because none of those premises are the premises I used in my argument. For fuck's sake will you please stop wasting everyone's time refuting arguments I'm not even making just because they have the same conclusions.

And your versions are not even representing what we're arguing about. They should go...

1. John knows that Joe Biden is President (and Joe Biden is a figment of John's mind)
2. Joe Biden is 79 years old (and being 79 years old is a figment of John's mind)
3. Therefore, John knows that Joe Biden is 79 years old (and 'knowing' anything is figment of John's mind, the 'truth' of anything means whatever john thinks is means because it's also a figment of John's mind)

or..

1a. X, Y and Z, all their properties, all their effects and all laws governing them are properties of John's mind because all there is is John's mind
1. John knows that X, Y, and Z exist and all other things that exist
2a. Jim (who is entertaining the possibility of such a world) knows that therefore...
2. If John claims "Only X, Y, and Z exist" - John cannot possibly be wrong because (unbeknownst to John), if John can't sense it, it doesn't exist. He only needs to check all he can sense to answer this question correctly, even if he doesn't know that's all he need do
3. Therefore, John knows that only X, Y, and Z exist (incorrect) but Jim knows such a world where John might exist is nonsense.

'All things it will cause' is a property of an entity. — Isaac

You're really reaching with what you mean by "property". I wouldn’t say that that the vase will fall off the table tomorrow and break is a property of the vase, or of the table, or of the floor, or of whatever.

But if you want to use the word "property" to refer to this sort of thing then I reject the assertion that solipsism entails that all "properties" of mental phenomena are known. See below.

1. John knows that Joe Biden is President (and Joe Biden is a figment of John's mind)
2. Joe Biden is 79 years old (and being 79 years old is a figment of John's mind)
3. Therefore, John knows that Joe Biden is 79 years old (and 'knowing' anything is figment of John's mind, the 'truth' of anything means whatever john thinks is means because it's also a figment of John's mind) — Isaac

Even if it is impossible for me to not know that I am in pain it is possible for me to not know that I have been in pain for 30 minutes. And this is true even if only my mental phenomena exists. I don't need for something other than my mind (e.g. another mind or a material universe) to exist for me to have been in pain for 30 minutes, or for me to not know that I have been in pain for 30 minutes.

There are facts about mental phenomena that might not be known even if the mental phenomena themselves are known.

2. If John claims "Only X, Y, and Z exist" - John cannot possibly be wrong — Isaac

He can possibly be wrong. I provided the argument several times:

Bp
¬□p
Bp ∧ ◇¬p

What you should say is:

2. If John claims "Only X, Y, and Z exist" - John is not wrong

All you have argued is that if ontological solipsism is correct then the ontological solipsist isn't wrong.

John knows that only X, Y, and Z exist (incorrect) — Isaac

If John doesn't know that only X, Y, and Z exist then he doesn't know everything.

Jim knows such a world where John might exist is nonsense. — Isaac

But it's not nonsense. It is a perfectly coherent situation. Only X, Y, and Z exist and they are all features of John's mind. He knows that X, Y, and Z exist but he doesn't know that only X, Y, and Z exist. He doesn't know what will exist in the future, or how X, Y, or Z will change. He might not know what existed in the past, given the limitations of memory. He might not know whether or not the Reimann hypothesis is true. He doesn't know what could have happened had he chosen a different course of action.

I wouldn’t say that that the vase will fall off the table tomorrow and break is a property of the vase, or of the table, or of the floor, or of whatever. — Michael

Then why did the vase fall off the table, if not because of some property of the world prior?

it is possible for me to not know that I have been in pain for 30 minutes. And this is true even if only my mental phenomena exists. I don't need for something other than my mind (e.g. another mind or a material universe) to exist for me to have been in pain for 30 minutes, or for me to not know that I have been in pain for 30 minutes. — Michael

I don't see how. What you say is true in our world because timekeeping is external and your memory is not always accessible to you. Two external features. I don't see how it would be the case in a world where all there was was your consciously aware mind.

He can possibly be wrong. I provided the argument several times:

Bp
¬□p
Bp ∧ ◇¬p — Michael

That's ignoring the implication of the entire world being in John's mind.

Only X, Y, and Z exist and they are all features of John's mind. He knows that X, Y, and Z exist but he doesn't know that only X, Y, and Z exist. He doesn't know what will exist in the future, or how X, Y, or Z will change. He might not know what existed in the past, given the limitations of memory. He might not know whether or not the Reimann hypothesis is true. He doesn't know what could have happened had he chosen a different course of action. — Michael

Those are the matters we're disagreeing over

That's ignoring the implication of the entire world being in John's mind. — Isaac

The rules of inference don’t change. You can only avoid the conclusion by rejecting one of the two premises. Either I don’t believe that ontological solipsism is true or ontological solipsism is necessarily true.

I don't see how. What you say is true in our world because timekeeping is external and your memory is not always accessible to you. Two external features. I don't see how it would be the case in a world where all there was was your consciously aware mind. — Isaac

Let’s assume that only my mind and your mind exist. I have been in pain for 30 minutes. According to your reasoning, either it is impossible for me to not know that I have been in pain for 30 minutes or that I have been in pain for 30 minutes is a property of your mind.

Or let’s assume that only my mind and seven billion other minds and a material universe of superstrings exist. I have been in pain for 30 minutes. According to your reasoning, either it is impossible for me to not know that I have been in pain for 30 minutes or that I have been in pain for 30 minutes is a property of one or more of these seven billion other minds, or of the material universe of superstrings.

I don’t think either of these scenarios make sense. So the conclusion is that either that I have been in pain for 30 minutes, although true, isn’t a “property” of anything, or something can be a “property” of my mental phenomena but not known.

Then why did the vase fall off the table, if not because of some property of the world prior? — Isaac

Because of stuff that happens in the future. I don’t understand what’s difficult to understand about this. Stuff that will happen in the future isn’t a “property” of things that exist in the present.

If only a material universe of superstrings exist it doesn’t follow that the future state of that universe is a property of that universe in the present. If only your mind and my mind exist it doesn’t follow that the future state of your mind is a property of your mind in the present (or a property of my mind in the present).

You can only avoid the conclusion by rejecting one of the two premises. Either I don’t believe that ontological solipsism is true or ontological solipsism is necessarily true. — Michael

Nonsense. You writing only two premises doesn't confer some kind of magical power. You've not listed all the premises which are being assumed by the argument.

Let’s assume that only my mind and your mind exist. I have been in pain for 30 minutes. — Michael

30 minutes has no meaning at all if only your mind and my mind exist. 30 of your minutes, or 30 of my minutes?

I don’t understand what’s difficult to understand about this. Stuff that will happen in the future isn’t a “property” of things that exist in the present. — Michael

It's not difficult to understand. I disagree. What's difficult to understand is why you can only seem to make sense of disagreements in terms of your interlocutors failing to understand something.

If only a material universe of superstrings exist it doesn’t follow that the future state of that universe is a property of that universe in the present. — Michael

Then what causes that future state?

Nonsense. You writing only two premises doesn't confer some kind of magical power. You've not listed all the premises which are being assumed by the argument. — Isaac

One of these is true:

1. Bp ∧ ◇¬p
2. Bp ∧ □p
3. ¬Bp ∧ ◇¬p
4. ¬Bp ∧ □p

Which of these is true if ontological solipsism is true?

One of these is true:

1. Bp ∧ ◇¬p
2. Bp ∧ □p
3. ¬Bp ∧ ◇¬p
4. ¬Bp ∧ □p

Which of these is true if ontological solipsism is true? — Michael

You haven't specified your terms. I can look up the notation, but I can't look up what you mean by Bp or p.

You haven't specified your terms. I can look up the notation, but I can't look up what you mean by Bp or p. — Isaac

p ≔ ontological solipsism is true
Bp ≔ I believe that p

So

1. I believe that ontological solipsism is true and it is possible that ontological solipsism is not true
2. I believe that ontological solipsism is true and ontological solipsism is necessarily true
3. I don't believe that ontological solipsism is true and it is possible that ontological solipsism is not true
4. I don't believe that ontological solipsism is true and ontological solipsism is necessarily true

...?

1. I think.

Why are you asking?

1. I think. — Isaac

Then you accept what I said here as part of this exchange:

2. If John claims "Only X, Y, and Z exist" - John cannot possibly be wrong — Isaac

He can possibly be wrong. I provided the argument several times:

Bp
¬□p
Bp ∧ ◇¬p

What you should say is:

2. If John claims "Only X, Y, and Z exist" - John is not wrong

All you have argued is that if ontological solipsism is correct then the ontological solipsist isn't wrong. — Michael

Then you accept what I said here as part of this exchange: — Michael

No. In my example, John is not the solipsist. John is a person in the possible world the solipsist is entertaining.