If the antirealist says we can know whether or not there is a god or a multiverse then they should be able to give an account of how that would be possible. — Janus

That’s not exactly what they’re saying. They’re saying that:

1. If “God exists” is true then it is possible to prove that it is true
2. If “God exists” is false then it is possible to prove that it is false
3. If it is not possible to prove that “God exists” is true and not possible to prove that “God exists” is false then “God exists” is neither true nor false

Dummett’s argument is that the disagreement between the realist and the antirealist concerns the logic of truth. For the realist, every proposition is either true or false. For the anti-realist, some propositions are neither true nor false.

And yet we obviously cannot know either of those. — Janus

It's not obvious to the anti-realist.

If your only "argument" against anti-realism is that it's "obviously" wrong then it's not an argument, just a denial.

A simple account would be to first argue that "'it is raining' is true" means "it is raining", and then to argue that "it is raining" is meaningful only if it describes a verifiable event. It would then seem to follow that "'it is raining' is true but unverifiable" makes no sense.

At least I believe that's the general gist of Dummett's antirealism.

The antirealists must be wrong though because they cannot rule out the possibility that unbeknownst to us there might be unknowable truths. Just stipulating that truths are only truths if they are known seems obviously wrong as it does not accord with the general notion of truth.

What if the question is changed to whether there are unknowable actualities instead? What about, for example, the question regarding the existence of God? We know we cannot know the answer to that, no matter how plausible or implausible the existence of God might seem. Would you say there cannot be a truth about whether or not God exists, despite that fact that it is obviously impossible to know? — Janus

You're just asserting that antirealism is "obviously" wrong. It's not obvious to the antirealist. The antirealist will argue that it is your "common sense intuition" that it wrong.

According to the antirealist, if God exists then we can know that God exists, and if God doesn't exist then we can know that God doesn't exist.

We know it is impossible to answer the question as to whether there is more than one unknowable truth. — Janus

This is the very thing that the anti-realist disagrees with. The ant-realist claims that we can know that there are no unknowable truths. In fact, the anti-realist claims that we do know that there are no unknowable truths. To many anti-realists, the very concept of an unknowable truth is incoherent. To many anti-realists, "X is true" means "X is verifiable".

But that has been shown to be false — Janus

No it hasn't.

What do you think the truth or falsity of "there are unknowable truths" is knowable means?

It means that one of these is true:

a) "there are unknowable truths" is true and we can know that it's true
b) "there are unknowable truths" is false and we can know that it's false

You haven't shown that (b) is false.

As an example to explain this, the truth or falsity of "there is a cat in the box" is knowable means that one of these is true:

c) "there is a cat in the box" is true and we can know that it's true
d) "there is a cat in the box" is false and we can know that it's false

so 1. must be true. — Janus

Yes.

The truth or falsity of "there are unknowable truths" is knowable.

The realist will say that it is knowable that "there are unknowable truths" is true.
The anti-realist will say that it is knowable that "there are unknowable truths" is false.

These are my (1) and (3) respectively.

I provisionally assume that "there are unknowable truths" is unknowable and then show that this leads to a contradiction, which shows it must be false. — Janus

Remember that there are four options, not two:

1. "there are unknowable truths" is knowably true
2. "there are unknowable truths" is unknowably true
3. "there are unknowable truths" is knowably false
4. "there are unknowable truths" is unknowably false

(4) is a contradiction so we can rule that out.

If (2) leads to a contradiction, as you say, then we can rule that out.

But that still leaves both (1) and (3). Your suggestion that if (2) is false then (1) is true is a non sequitur.

However if the starting assumption is that the truth or falsity regarding the existence of unknowable truths is unknowable then we know that there is at least one unknowable truth. — Janus

You assume "there are unknowable truths" is unknowable and then conclude "there are unknowable truths" is knowable.

This is still a contradiction.

You must pick one of these:

1. "there are unknowable truths" is unknowable
2. "there are unknowable truths" is knowable

If you pick (1) then you cannot conclude (2).
If you pick (2) then you cannot use (1) to justify it.

What about all the truths regarding what happened in the pre-human past? Are they unknowable? You might say they are not unknowable in principle. — Janus

They will likely say that propositions about the past are neither true nor false because they (and their negations) are unverifiable.

Fair, so I suppose I should "if P then Q" means "not-P or Q or both".

However if it is right that the truth or falsity regarding the existence of unknowable truths is unknowable then we know that there is at least one unknowable truth. There is no contradiction — Janus

That is literally a contradiction.

The first part in bold is saying that "there are unknowable truths" is unknowable and the second part in bold is saying that "there are unknowable truths" is knowable.

If there is a truth as to whether there are unknowable truths, then that truth is an unknowable truth. So we know there is at least one unknowable truth. If you think there is something wrong with the reasoning, then say what it is. — Janus

I explained it in that previous post.

You go from a) "there are unknowable truths" is unknowably true to b) "there are unknowable truths" is knowably true. This is a contradiction. If (a) is true then (b) is false and if (b) is true then (a) is false.

A ⊻ ¬A ↔ A ∨ ¬A

I have shown that we know there is at least one unknowable truth. — Janus

No you haven't. You've just asserted it, hence why you are begging the question.

My point is that we know that If P then Q, where P = A and Q = not-A, implies a contradiction where P is true because Q will be true and both A and not-A will be the case. — Benkei

"If P then Q" means "not P or Q".
"If A then not A" means "not A or not A".

"not A or not A" is not a contradiction.

It is counterintuitive to assert that "if it rains then it doesn't rain" and "it rains" therefore "it doesn't rain" is a valid argument. — Benkei

"If it rains then it doesn't rain" means "it doesn't rain or it doesn't rain".

So the argument is:

P1. it doesn't rain or it doesn't rain
P2. it rains
C1. therefore, it doesn't rain

Notice that P1 and P2 cannot both be true. If P1 is true then P2 is false; if P2 is true then P1 is false.

C1 is irrelevant. It could be anything, as per the principle of explosion.

Well, if you're talking about practical enforcement then I suppose it's the armed forced which has the final say.

A constitutional amendment requires two-thirds of both houses and three quarters of the states.

Well, he certainly can't be elected again. That would require a constitutional amendment which ain't happening.

A grey area is if he is nominated as Speaker of the House (which doesn't require being a congressman), and then having the President and Vice President resign.

So don't worry, there might be a way to get Obama back.

What? And end up with the same insanity as the USA? — Benkei

It's cool, we're better than them. I'd suggest letting the Scandinavians take the lead, they seem to know what they're doing.

Answer the question I posed: Do you think it is possible to know whether the claim that there are unknowable truths is true? — Janus

I don't have a position, but here are the options:

1. "there are unknowable truths" is knowably true
2. "there are unknowable truths" is unknowably true
3. "there are unknowable truths" is knowably false
4. "there are unknowable truths" is unknowably false

Anti-realists believe (3). (4) is a contradiction.

That leaves you with either (1) or (2).

If (1) is true then (2) is false and so you cannot use (2) to justify (1), which is what you appear to be trying to do.

It is obviously impossible even in principle. because no matter how many truths we know there could always be an unknowable truth. — Janus

This is begging the question.

“All truths are knowable” cannot be unknowably true.

Therefore one of these is true:

1. “All truths are knowable” is knowably true
2. “All truths are knowable” is false

The anti-realist believes (1) and the realist believes (2).

You haven’t justified (2), only asserted it.

You haven’t shown it. You just asserted it.

We know that we can't know the truth as to whether all truths are knowable because no matter how many truths we know we have no way of knowing whether there are further truths that are unknowable. — Janus

You’re just asserting that some truths are unknowable.

Can you justify the part in bold? If not then you haven’t shown that (5) is true.

I'd support a USE.

I wonder who Trump will install as FBI director, after he fires Christopher Wray. — Relativist

The same Christopher Wray he appointed?

This is is also likely to be overturned. — Relativist

I believe the appeal has been rescinded as Jack Smith is resigning so we won't get a decision on the matter. It's moot.

Here's a scenario:

P1. Only John exists
P2. John believes that something other than himself exists
C1. Therefore, John holds a false belief
P3. (optional) It is impossible for John to disprove this false belief

Is this realism or anti-realism (with or without P3)? Normally we might think of solipsism as being anti-realism, but it involves something like a correspondence theory of truth (and optionally an unprovable truth).

Maybe we do need to distinguish between metaphysical realism and semantic realism. The former may entail the latter but the latter does not entail the former.

But to offer a more substantive response, one of these is true:

1. "all truths are knowable" is true and knowable
2. "some truths are unknowable" is true and knowable
3. "some truths are unknowable" is true and unknowable

If knowledge is justified true belief then one of these is true:

4. "all truths are justifiable" is true and justifiable
5. "some truths are unjustifiable" is true and justifiable
6. "some truths are unjustifiable" is true and unjustifiable

The interesting thing about (6) is that if it's true then realism is both true and unjustifiable. Technically that's consistent with realism, but perhaps not of much comfort to the realist who seeks to justify his position.

So pragmatically that leaves us with (4) and (5). How do we decide between them without knowing any unknown truths?

How can the anti-realist justify the claim that all unknown truths are knowable? You would have to know them to know they are knowable, no? — Janus

How can the realist justify the claim that some unknown truths are unknowable? You would have to know them to know they are unknowable, no?

Hence, if something can be true then it is possible to know that it is true. Hence, the antirealist knows everything that is true. — Banno

And as mentioned before, the antirealist rejects the conclusion. They might claim that every truth is knowable but that some truths are unknown.

It's not enough for antirealists just to say they reject the entailment. Some explanation is needed. — Banno

They do, e.g. by adopting intuitionist logic.

This is simply a restatement of the antirealist thesis that something can be true only if it has been demonstrated. — Banno

That's not the antirealist thesis. The antirealist thesis is that something is true only if it can be demonstrated. You are, again, treating the critic's conclusion as the proponent's claim.

But as a question to you, do you believe that all mathematical truths are known? You claimed in an earlier post that you are a mathematical antirealist.

I think a simple solution is to use a restricted knowability principle:

∀p∀q((p ⊭ (q ∧ ¬Kq)) → (p → ◊Kp))

For all p that doesn't entail that some q is an unknown truth, if p is true then p is knowable.

Which makes sense. If knowing p is a contradiction (which knowing an unknown truth is) then it’s not possible to know p, but if knowing p is not a contradiction (and if p is true) then it is possible to know p.

I'd say that this is still antirealism.

Matt Gaetz as attorney general? Jesus, I'm laughing. What a joke this whole thing is. :lol:

Wasn't he the one who paid that 17 year old for sex?

Not following that. — Banno

Well, let's take the SEP article:

Fitch’s paradox of knowability (aka the knowability paradox or Church-Fitch Paradox) concerns any theory committed to the thesis that all truths are knowable. Historical examples of such theories arguably include Michael Dummett’s semantic antirealism (i.e., the view that any truth is verifiable), mathematical constructivism (i.e., the view that the truth of a mathematical formula depends on the mental constructions mathematicians use to prove those formulas), Hilary Putnam’s internal realism (i.e., the view that truth is what we would believe in ideal epistemic circumstances), Charles Sanders Peirce’s pragmatic theory of truth (i.e., that truth is what we would agree to at the limit of inquiry), logical positivism (i.e., the view that meaning is giving by verification conditions), Kant’s transcendental idealism (i.e., that all knowledge is knowledge of appearances), and George Berkeley’s idealism (i.e., that to be is to be perceivable).

...

The great problem for the middle way is Fitch’s paradox. It is the proof that shows (in a normal modal logic augmented with the knowledge operator) that “all truths are knowable” entails “all truths are known”.

So the anti-realist doesn't claim that all truths are known, only that all truths are knowable. Fitch attempts to refute this by showing that this entails that all truths are known (which is taken to be an obvious falsehood), but this is an entailment that (some) anti-realists will reject.

I was mostly addressing this:

if the only things that are true are the things that we know to be true — Banno

The claim is that the only things that are true are things that can be known to be true. Fitch may attempt to prove that this entails that we know everything, but it's important to properly represent the actual claim being made by the anti-realist.

You mention Fitch's paradox, which is also an argument against mathematical constructivism, and as you said in an earlier post, "I have however also defended a constructivist view of mathematics, an anti-realist position".

Presumably you accept that we don't know everything about maths.

And I should clarify, you talk about "all truths being known" in reference to Fitch's paradox, but the relevant claim under consideration is "all truths are knowable", a subtle but important difference.

But of course, as with your own example of maths and aesthetics, one can be an anti-realist about some things but not about others. So perhaps global anti-realism entails Fitch's paradox, but anti-realism about medium-sized dry goods (and mathematics) doesn't.

You mean my brain is alive in her body. — NOS4A2

And there is a person. That person remembers growing up as you, not as Jane. Your claim is that this person is Jane because it's Jane's body and my claim is that this person is you because it's your brain (and memories and personality and so on).

I think that my view is more reasonable than your view.

But your brain is still alive. If a person is a brain, and the brain is still alive, the person is still alive, no? — NOS4A2

As I said above, I am a single person. If my brain is cut in half and each part kept alive and put in two different bodies then there are now two people. Given that I am not two people and given that neither new person is privileged, it must be that neither of these two people are me, and so I am dead.

The same reasoning applies to your claim that the organism is the person; if your body is cut in half and each half kept alive by replacement organs then there are now two organisms, not one. You cannot be both, therefore either neither is you or one of them is privileged. But at least in this case I would say that the half that kept the brain is the privileged half and so is you; the other half is just a bunch of organs, not a person.

It’s why you cannot imagine yourself being a disembodied brain without some sort of mechanism to keep you alive while you’re outside the body. — NOS4A2

I certainly could imagine it. It's just not biologically feasible as a brain cannot survive without help.

Relevant to this is this:

Decapitation is quickly fatal to humans and most animals. Unconsciousness occurs within seconds without circulating oxygenated blood (brain ischemia). ... ("[Consciousness is] probably lost within 2–3 seconds, due to a rapid fall of intracranial perfusion of blood").

A laboratory study testing for humane methods of euthanasia in awake animals used EEG monitoring to measure the time duration following decapitation for rats to become fully unconscious, unable to perceive distress and pain. It was estimated that this point was reached within 3–4 seconds, correlating closely with results found in other studies on rodents (2.7 seconds, and 3–6 seconds). The same study also suggested that the massive wave which can be recorded by EEG monitoring approximately one minute after decapitation ultimately reflects brain death. Other studies indicate that electrical activity in the brain has been demonstrated to persist for 13 to 14 seconds following decapitation (although it is disputed as to whether such activity implies that pain is perceived), and a 2010 study reported that decapitation of rats generated responses in EEG indices over a period of 10 seconds that have been linked to nociception across a number of different species of animals, including rats.

There is, perhaps, at least a few seconds where the brain is alive (and a conscious person).

I don't see any difference between "being used as a cup" & "having potential for being used as a cup" , both carry the same purpose as far as they allow us to group objects under a universal like "cup" — Sirius

"So-and-so is a wife only if she has been legally married" does not mean "so-and-so is a wife only if she has the potential to be legally married".

Some might say that the mere potential to be seen or used as a cup is insufficient to be a cup; it has to actually be seen or used a cup.

I'm not sure what the distinction is doing here at all. You introduced it. But presumably, extensionally, X is a cup if and only if X is a cup. — Banno

According to some anti-realists, X is a cup only if it stands in a certain kind of relationship with us, just as X is a king only if it stands in a certain kind of relationship with us.

Simply saying that X is a cup if and only if X is a cup or that X is a king if and only if X is a king is vacuous, and doesn't address any philosophical dispute.

I am hunting around for something to tie down your idea. — Banno

Much like "there is no king if the monarchy is abolished" does not mean "Charles ceases to exist if the monarchy is abolished", "there is no cup if none is seen" does not mean "the extensional object ceases to exist if it is no longer seen". You seem to be pushing this latter misrepresentation, treating all anti-realisms as phenomenalism.

Not so much, perhaps, since "This has nothing to do with scientific realism" yet " it's perfectly consistent with physicalism and scientific realism". — Banno

"John is a man" being true is consistent with but has nothing to do with "Jane is a woman" being true.

I gather this is intensional, as opposed to extensional. — Banno

I'm not sure how that distinction applies to that premise.