Blimey. Where to start? To cut to the chase, no, the argument (as stated) is not valid, but could become so if additional premises are included. It's also worded unusually, (poorly, in my view). I think that you should lose the "only" as it seems redundant.

The premise, in the sense in which I believe you meant it, is a truism, and perhaps a tautology, and would be absurd to deny. I can think of a possible exception, in that we can and do think of things from the perspective of another. In fact, it's valuable to do so, especially in philosophy. But I don't think that that's what you meant.

It simply doesn't follow, from that premise alone, that all things are things that I think, even if you add the rather pointless qualification "from my perspective". I accept the premise, but reject the conclusion, and no contradiction arises as a result. Things that I think are merely a subset of things. The aforementioned statement is one which I believe to be true, not only from my perspective, but irrespective of it. That underlined statement implies that I maintain (and rightly so) that, at any given time, there are things of which I do not think.

Why is "what exists from my perspective" equated with "what exists?"

Because we are interested in what exists FOR YOU. From your perspective everything is from your perspective!

Isn't it just a logical argument though?

1. All and only (things that you think) are (from your perspective.)

therefore

2. All (from your perspective) are (things are things you think.)

It is just

1. All and only As are Bs.
2. All Bs are As.

That's valid isn't it?

Because we are interested in what exists FOR YOU. From your perspective everything is from your perspective! — invizzy

That would seem to imply solipsism, not idealism.

Additionally, I don't think we ought to give ultimate primacy to individual perspective.

Well, first of all, I'll note that you've altered the argument in such a way that my original criticism might no longer apply. So, I'll start from scratch.

Seems valid, but even if so, it seems trivial, and idealism doesn't follow from that alone, so I hope that you have more up your sleeve. You'd have to end up with a conclusion along the lines of: all things are things-that-I-think. (Which differs significantly from the conclusion that all things-from-my-perspective are things-that-I-think). If your next step is to add the premise that all things are things-from-my-perspective, then that'll be where your argument fails.

Like Pneumenon, I'm not sure if "idealism" best sums up the position that you're arguing for. He said solipsism, whereas I was thinking relativism, although solipsism implies relativism. Do you accept the existence of other minds? Do you think that all is relative? Or (at least) that all truth is relative?

But all my claims are going to be from my perspective. Indeed it is impossible to make claims any other way.

If
All (from your perspective) are (things you think.)
then I should be able to truthfully utter

"All are things you think."

Which is indeed my claim.

In that case, my perspective doesn't exist. Only yours does.

How so?

You can't make a claim from my perspective, only from your own. Therefore, anything in my perspective that isn't in yours (including my sensations and such) don't exist. Thus, I don't have a mind. Only you do.

Yes that's true. From my perspective.

But all my claims are going to be from my perspective. Indeed it is impossible to make claims any other way. — invizzy

You seem to think that that's in some way significant. The key word here, which you've thus far neglected, is dependency. Implicitly, I make claims from my perspective, but whether or not the truth-value of any given claim is dependent on my perspective is the salient issue.

If
All (from your perspective) are (things you think.)
then I should be able to truthfully utter

"All are things you think."

Which is indeed my claim. — invizzy

No, that'd only follow if all is from my perspective, but that isn't the case, and you haven't provided an argument for that claim in this thread. The burden of proof lies with you if that's what you're going to claim.

Your argument would be as follows:

P1. Everything from a person's perspective is a thing that is thought of.
P2. Everything is a thing from a person's perspective.
C. Therefore, everything is a thing that is thought of.

That's a valid syllogism, but it contains at least one false premise, viz. P2, and is therefore unsound.

Edit

All (from your perspective) are (things you think.) — invizzy

Come to think of it, I think I might have misread the above. I read it as:

(All from my perspective) are (things that I think).

But:

All (from my perspective) is things that I think

...Is the same as if I claimed:

All is things that I think.

...But I wouldn't claim that, because it's false. All is everything, not just things that I think.

And your perspective is all there is. But now I foresee a retreat to "But my perspective is all there is from my perspective!" which is just a tautology.

But all my claims are going to be from my perspective. Indeed it is impossible to make claims any other way. — invizzy

Yes that's true. From my perspective. — invizzy

Also, your position is self-defeating. With statements like the above, we can ask whether they are relative or absolute. If relative, then the statement does not rule out absolutes. So, for example, you'd have to conede that it is possible to make claims in other ways, and that it might not just be true from your perspective, but true absolutely. (And we can take the reducio ad absurdum even further. E.g. you wouldn't actually be able to consistently claim that anything is impossible in an absolutist sense, which is the only sense in which impossibility makes sense. And if you can't consistently claim that anything is impossible in a meaningful way, then goodbye fundamental laws of thought and rational discourse). If the statement is absolute, on the other hand, then it provides an example of an absolute statement, proving that not all truths are relative.

But now I foresee a retreat to "But my perspective is all there is from my perspective!" which is just a tautology. — Pneumenon

No, that'd only follow if all is from my perspective, but that isn't the case, and you haven't provided an argument for that claim in this thread. — Sapientia

Sorry because it WAS a tautology I thought it trivially true and didn't include it in the premises. But surely it is true:

P. Everything from your perspective is from your perspective.

Tautological, yes. True? Of course.

And it is not self-defeating. We still have absolute truth, there IS absolute truth from your perspective. We can still be objectively wrong for instance.

An argument that does not have at least one non-tautological premise fails to yield a non-trivial conclusion.

It's also an admission of their own wilful ignorance.

If I hold the position I am talking to a different person, my perspective holds it does not exhaust reality. You, who is not me, who is not my perspective, is present. To then say: "but from my perspective there is only my perspective" is to ignore what I know about the world. It is to pretend the world is nothing more than matter of my perspective when I know very well it isn't.

But it does.

P1. All and only (things that you think) are (from your perspective.)

together with the new tautological premise:

P2. All (from you perspective) is (from your perspective)

C. All (from your perspective) are (things are things you think.)


It is just

P1. All and only As are Bs.
P2. All Bs are Bs.
C. All Bs are As.

Things from my perspective can be thoughts, sensations, or the room I'm sitting in. The latter two are not things that I think. Of course, I'm guessing you'd get around this by saying that you're using a different definition of "things that you think" or "from your perspective." But if you're just changing the definitions of "thought" and/or "perspective" in order to make them equivalent, then you haven't demonstrated anything.

P1. and C are useless there.

You already said everything in C. in P1. (all and ONLY As are Bs- i.e. The entire set of B is As).

P2. is just a meaningless tautology. Of course, Bs are Bs. That's the identity of B. It isn't driving any so of conclusion about because nothing is premised upon it.

Um... of course I need P1, that's my argument. Otherwise I'd just be asserting C.
Now I agree P2 is a tautology, that's why I didn't have it originally. Others in this thread thought I needed it.

My point is that C. is merely a restatement of P1. You are merely asserting P1./C.

P2 doesn't give any conclusion about either A or B. You don't have a valid argument. All you have is a stated premise: "Set of As are the entire set of Bs" (P1./C1) and an irrelevant tautology "B=B" (P2).

There is no argument or reasoned conclusion.

Right. So you agree that the argument is valid, now you're just questioning P1., specifically whether there can be things from your perspective that are not mental? Actually, if I phrase it as 'mental' does that hold seeing it covers sensations?
Now I'm not entirely sure a room itself can be from your perspective, I would suggest only the thought of the room can. Do inanimate objects have perspectives as such?

So a room can't be from your perspective. But, vis a vis your earlier argument, everything is from your perspective. Ergo, rooms don't exist.

Pretty sure

P1. All and only As are Bs

is different to

C. All Bs are As

Isn't it a syllogism? It is worked out logically i.e. not by observation. How exactly do you think logical arguments are meant to work if not like that?

Yeah that's my claim, only thoughts exist.

So "think" and "perspective" drop out, and you're left with the premise, "Everything that is mental is mental." From this, you derive that everything is mental simpliciter.

They aren't.

P1. says the same thing as C. through the "only." Since only As are Bs, you've already said all Bs are As. If there was to be a B which is not an A, it would mean it was not only As which are Bs.

Given P1., there is no possibility of a B which is not an A. C. does no work because you've already removed any possibility of a B which is not a A in P1.

Hence why it is a logical argument.

So "think" and "perspective" drop out, and you're left with the premise, "Everything that is mental is mental." From this, you derive that everything is mental simpliciter. — Pneumenon

Not quite sure what you mean here. Is that a question?