My comments about truth being a single-placed predicate are intended to show that there are uses for assigning truth to sentences outside of our attitudes towards them. I've highlighted these elsewhere -

Surprise
We are sometimes surprised by things that are unexpected. How is this possible if all that is true is already known to be true?

Agreement
Overwhelmingly, you and I agree as to what is true. How is that explainable if all there is to being true is attitudes? How to explain why we share the same attitude?

Error
We sometimes are wrong about how things are. How can this be possible if all that there is to a statement's being true is our attitude towards it? — Banno

But constructivism doesn’t entail that there are no facts outside our knowledge of them. I see the point about constructivism as being, not that there can’t be unknown facts, but that whatever facts we come to know are incorporated into the way we construe the totality of experience, our worldview. Or not, in which case we might have to change it. That we are not passive observers of an already-existing world but are active participants in it.

Constructivism Lite. Clayton's constructivism - the constructivism you have when you are not a constructivist.

Sure, why not.

So what’s the full- strength version?

I'm not defending it. Someone else can give an account, if they want.

Constructivism is nonetheless a counterpoint to realism, is it not?

You tell me. We are talking about realism and antirealism. You brought in constructivism. Set it up for us, if you like.

Is this the second Warble, or the third? The gonad is in your corner.

It’ll have to wait, but I will.

See you after the umlaut.

What is it about antirealism that you have to say? — Banno

The first thing is that it isn't any of your strawmen. Antirealism doesn't claim, and nor do antirealists acknowledge that it entails, that all truths are known.

The second thing is that it is consistent with a deflationary account of truth.

The third thing is that it avoids certain absurdities that realism allows for, e.g. that it is possible that we are unknowably brains in a vat.

The fourth thing, albeit directed at Janus, is that it is not obviously wrong.

Antirealism doesn't claim, and nor do antirealists acknowledge that it entails, that all truths are known. — Michael

Depends on what truth is, as such. The antirealist generally considers truth, the stand-alone conception in itself, in A59/B84, 1787, to be the agreement of an object with the cognition of it, re: ’s active participant thesis. Also, Putnam, 1988: “…Truth involves some correspondence relation between words or thought-signs and external things…”.

Given that no cognition is unknown to the subject that thinks it, and given the cognition corresponds without contradiction to the object to which it is related, then it must be the case the relation is itself a object of knowledge, which is just to say it is known to the subject, and it is by this means alone that the criterion for the definition of truth is satisfied, and from which follows that all truths are known.

Some musings.

Let's take the knowability principle from Fitch's paradox: ∀p(p → ◊Kp).

According to this, "a marker of necessity functions as a universal quantifier: it indicates that the basic proposition is true in all possible states of affairs. A marker of possibility functions as an existential quantifier: it indicates that there is at least one state of affairs in which the basic proposition is true."

So the knowability principle can be rephrased as:

□(p → ◊Kp)

The realist rejects this knowability principle.

But under S5 ¬□(p → ◇Kp) → □¬Kp.

So if the knowability principle is false and if S5 is correct then nothing is knowable (and so nothing is known)?

and from which follows that that all truths are known. — Mww

Well, no.

The antirealist argues that if "the cat is in the box" is true then it's possible for someone to know that it's true, e.g. by looking in the box and seeing the cat. The fact that it's possible for someone to look in the box and see the cat does not entail that someone already knows that the cat is in the box: perhaps nobody knows because nobody’s looked.

The realist argues that "the cat is in the box" can be true even if it's not possible for someone to look in the box and see the cat.

Which is more reasonable? I say the former. The latter arguably doesn't even make sense. What does it mean for it to be not possible for someone to look in the box and see the cat (despite the cat being in the box)? Looking in the box and seeing the cat is certainly not a contradiction, so it can't be that.

Ehhhh…..the continental antirealist in general will only go so far as to say if the cat’s in the box, fine; if the cat’s not in the box, that’s fine too. If I’m interested enough, if it’s important enough, to know which, I’ll go look for myself.

Antirealism doesn't claim, and nor do antirealists acknowledge that it entails, that all truths are known. — Michael

Sure. And they do this by rejecting classical logic.

The second thing is that it is consistent with a deflationary account of truth. — Michael

Yep.

The third thing is that it avoids certain absurdities that realism allows for, e.g. that it is possible that we are unknowably brains in a vat. — Michael

Realism does not commit to vat brains. This is an odd objection.

The fourth thing, albeit directed at Janus, is that it is not obviously wrong. — Michael

Sure.

Is any of this inconsistent with what I have said?

We are talking about realism and antirealism. You brought in constructivism. — Banno

I think the term 'antirealism' can sometimes be misleading. The key point about so-called antirealism, as I see it, is that it challenges the tenet of mind-independence as the criterion for what is real—the idea that what is the case exists entirely irrespective of any perspective or knowledge of it.

I brought up constructivism because it incorporates aspects of idealism while stopping short of claiming that reality is mental or mind-like in nature. Constructivism emphasizes the role of human activity, interpretation, and social practices in constructing knowledge, reality, and meaning.

Realism, in contrast, seems grounded in an empirical attitude: the world is just so, and knowledge discloses its nature through continued discovery. Constructivism, ultimately, harks back to Kant and his Copernican Revolution in philosophy—the idea that things conform to thoughts, and not vice versa.

Let's take the knowability principle: ∀p(p → ◊Kp). — Michael

I appreciate the breakdown of the knowability principle and the use of modal logic to clarify these issues. Modal logic is a topic I’ve started to learn about through this forum, and I appreciate the rigor. That said, my interests lie more in the existential dimension—how the mind constructs and relates to reality in a lived, phenomenological sense. I see these questions as tied to insight and transformation, which may not be completely amenable to analysis through symbolic logic. Modal logic, by its nature, focuses on propositional structures, and I think that’s where the divergence in our perspectives lies.

Sure. And they do this by rejecting classical logic. — Banno

Well, yes. That’s how Dummett defined the distinction between realism and antirealism; realists commit to the classical logic of bivalence and antirealists reject it.

Realism does not commit to vat brains. — Banno

It entails their possibility. Antirealism provides an opportunity to dismiss the notion as nonsense.

So you think you need antirealism to avoid being a vatted brain. Right.

So you think you need antirealism to avoid being a vatted brain. Right. — Banno

These mean different things:

1. We are brains in a vat
2. It is possible that we are brains in a vat

In propositional logic:

1. P
2. ◊P

If realism is correct then (2) is true. Putnam argues that (2) is false and so that therefore realism is incorrect.

Repeatedly you either fail to understand or intentionally ignore the distinction between what is said to be true (or known, or proved) and what is said to be possibly true (or knowable, or provable).

The problem with realism is that it entails this kind of global skepticism. If there are unknowable truths then there are unjustifiable truths, and if there are unjustifiable truths then a proposition not being justified is not a good reason to reject it. — Michael

This is not right. You are trying to claim that it follows from your premises that there are truths which are both known and unjustifiable, and this does not follow.

Or in other words: one accepts or rejects truth-claims on the basis of justification, not irrespective of justification. One has good reason to dismiss a truth-claim if it lacks justification; and the absence of justification is never, in itself, a good reason to deem a proposition false.

Edit: Or, "...then a proposition not being justified is not a good reason to reject it." There is an equivocation here on 'reject'. If 'reject' means falsify, then this strikes me as uncontroversial. If 'reject' means "abstain from affirming," then the consequent is false but it does not in fact follow from your premises.

I think the term 'antirealism' can sometimes be misleading. — Wayfarer

I got one for you, for a change. Hopefully not overly simplistic.

“….Most writers on the topic agree, as the name suggests, antirealism is defined in contrast to realism: antirealism is not what realism is. In J. L. Austin’s phrase, realism wears the pants of the pair…”
(Braver, “Thing of This World”, 2007)

https://books.google.com/books?id=YIGHyP3tesC&pg=PA13&source=gbs_toc_r&cad=2#v=onepage&q&f=false

You are trying to claim that it follows from your premises that there are truths which are both known and unjustifiable — Leontiskos

I'm not.

I'm trying to explain this:

One proposal is to construe metaphysical realism as the position that there are no a priori epistemically derived constraints on reality (Gaifman, 1993). By stating the thesis negatively, the realist sidesteps the thorny problems concerning correspondence or a “ready made” world, and shifts the burden of proof on the challenger to refute the thesis. One virtue of this construal is that it defines metaphysical realism at a sufficient level of generality to apply to all philosophers who currently espouse metaphysical realism. For Putnam’s metaphysical realist will also agree that truth and reality cannot be subject to “epistemically derived constraints.” This general characterization of metaphysical realism is enough to provide a target for the Brains in a Vat argument. For there is a good argument to the effect that if metaphysical realism is true, then global skepticism is also true, that is, it is possible that all of our referential beliefs about the world are false. As Thomas Nagel puts it, “realism makes skepticism intelligible,” (1986, 73) because once we open the gap between truth and epistemology, we must countenance the possibility that all of our beliefs, no matter how well justified, nevertheless fail to accurately depict the world as it really is. Donald Davidson also emphasizes this aspect of metaphysical realism: “metaphysical realism is skepticism in one of its traditional garbs. It asks: why couldn’t all my beliefs hang together and yet be comprehensively false about the actual world?” (1986, 309)

I try to prove an even stronger version of this using propositional logic here.

I'm not.

I'm trying to explain this: — Michael

I know, and your argument is invalid. I explained why. We can agree with Nagel's quote, and yet your argument remains invalid. You are conflating the possibility of skepticism with skepticism.

You are conflating the possibility of skepticism with skepticism. — Leontiskos

I'm not sure what you think I'm arguing, or what you mean by the possibility of skepticism.

The skeptic doesn't say "we are brains in a vat"; the skeptic says "we might be brains in a vat". Something like "it is possible that we might be brains in a vat" is redundant, as, at least using S5 modal logic, ◇◇P↔◇P.

This is not a valid argument:

If there are unknowable truths then there are unjustifiable truths, and if there are unjustifiable truths then a proposition not being justified is not a good reason to reject it. — Michael

I gave reasons above.

I gave reasons above. — Leontiskos

But your reasoning is not directed at what I was claiming. You said "you are trying to claim that it follows from your premises that there are truths which are both known and unjustifiable".

I'm not trying to claim that, because that claim would be a contradiction.

If there are unknowable truths then there are unjustifiable truths, and if there are unjustifiable truths then a proposition not being justified is not a good reason to reject it. — Michael

Or, "...then a proposition not being justified is not a good reason to reject it." There is an equivocation here on 'reject'. If 'reject' means falsify, then this strikes me as uncontroversial. If 'reject' means "abstain from affirming," then the consequent is false but it does not in fact follow from your premises. — Leontiskos

This proposition is true:

1. We do not have evidence that we are brains in a vat

If realism is correct then this proposition is true:

2. It is possible that we are brains in a vat and that we cannot have evidence that we are brains in a vat

My suggestion is that if we cannot have evidence that we are brains in a vat then (1) does not sufficiently justify the claim that we are not brains in a vat.

My suggestion is that if we cannot have evidence that we are brains in a vat then (1) does not sufficiently justify the claim that we are not brains in a vat. — Michael

What do you mean by "sufficiently"?

"to an adequate degree"?

That doesn't help. Your argument rides on the vagueness of that word.

Consider:

This proposition is true:

1. We do not have evidence that there is no teapot orbiting the Sun

If realism is correct then this proposition is true:

2. It is possible that there is a teapot orbiting the Sun and that we cannot have evidence that there is a teapot orbiting the Sun

My suggestion is that if we cannot have evidence that there is no teapot orbiting the Sun then (1) does not sufficiently justify the claim that there is no teapot orbiting the Sun. — substitution

You might say that there is a difference between physical possibility and metaphysical possibility, but I think the same point holds with each.