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.

It is rather hard to see how "a cup exists only if there exists some X such that X is being seen or used as a cup" counts as scientific realism. — Banno

I explained it quite clearly in that post:

P1. A cup exists if and only if there exists some X such that X is a cup
P2. For all X, X is a cup only if X is being seen or used as a cup
C1. Therefore, a cup exists only if there exists some X such that X is being seen or used as a cup

Much like a king exists only if there exists some X such that X is [insert necessary social conditions here].

Do you believe that the argument is invalid, or do you reject one or both premises?

This has nothing to do with scientific realism, which only claims that the entities described by our scientific theories (e.g. the particles of the Standard Model) exist mind-independently (and behave as our models say they do).

Science says nothing about what it means to be a king or what it means to be a cup.

There's a reason that a "brain transplant" is also called a "whole-body transplant".

https://en.wikipedia.org/wiki/Brain_transplant

A brain transplant or whole-body transplant is a procedure in which the brain of one organism is transplanted into the body of another organism ... Theoretically, a person with complete organ failure could be given a new and functional body while keeping their own personality, memories, and consciousness through such a procedure.

I think this is the proper way to understand it.

I doubt she remembers anything. She’d have to form new memories. — NOS4A2

The brain has all the connections it had before it was removed from your body, so she will have your memories.

And I think that's absurd. It's not the case that Jane forgets her life and remembers yours; it's the case that Jane is dead and you're alive in her body.

You cut it in half. — NOS4A2

Yes, and in doing so it became two organisms, such as what happens naturally with some worms.

So how did you as a person die if both halves of your brain survived and were placed in two different heads? — NOS4A2

I can't be a single person in two disconnected bodies with two disconnected brains, and neither half is somehow privileged such that one is me and the other isn't. So it must be that neither is me. Therefore I'm dead.

I just don’t see how I would die if I was still alive after such a procedure. — NOS4A2

You wouldn't still be alive, you'd be dead. The body would still be alive, but the body isn't you. The body now belongs to someone else (the person whose brain replaced yours).

I've never been a brain. My memories and personality have only ever related to a certain organism. — NOS4A2

That doesn't answer my question. Jane's brain is removed and replaced with yours. According to you, it's still Jane. But given that memories are stored in the brain, it would then follow that Jane no longer has her (original) memories and instead has yours. So she remembers growing up as a boy named [your name] rather than as a girl named Jane.

I would remain as one organism, except I'd be one that's been cut in half. So I guess I'd have to choose both sides as me. — NOS4A2

But there are two unconnected bodies. How can they be one organism?

How would you die? Split-brain patients can live through such a procedure. — NOS4A2

"Split brain" patients aren't fully split. They are still joined at the stem. It's only the connection between the hemispheres that is removed.

I wouldn't because it would be extremely painful and debilitating. I would choose death before that. But if I did I don't think I'd be numerically identical to someone else. — NOS4A2

In this scenario it isn't extremely painful and debilitating. We're advanced enough that it's like a kidney transplant.

But my point is that it would be death, so it's not a choice between living (in pain) or dying; it's a choice between dying of brain cancer or dying of brain extraction-and-destruction, i.e. you're opting for euthanasia.

The body that's kept alive by a new brain just ain't you.

What if they could upload your consciousness and store it until the new body is ready? — frank

An upload is just a copy, it's not me. It's not like there's some physical substance that is literally removed from my brain and placed on a computer for safekeeping.

I'm curious; let's assume that brain transplants are possible and easy and that you have been diagnosed with terminal brain cancer. Would you accept a brain transplant as a cure (with your diseased brain being destroyed)?

Because I certainly wouldn't. I understand that this would mean my death.

I would be deceased. Jane would identify as Jane because it is Jane that is still surviving, still alive. I say this because one’s person’s body, via the immune system, would reject the other’s. I suspect that it would be Jane’s immune system rejecting my tissue, meaning my tissue is foreign, ie. not of the person. — NOS4A2

So, for you, a brain transplant is a memory and personality transplant? Jane receives your brain and with it loses her memories and personality but gains yours in their place?

So long as the survival of the organism or animal is maintained I remain the same organism or animal. — NOS4A2

What counts as an organism?

We've mentioned before that there are five "vital" organs; brain, heart, lungs, liver, and kidneys. At the very least we both appear to accept that we can replace the heart and still be the same person, replace the lungs and still be the same person, replace the liver and still be the same person, and replace the kidneys and still be the same person.

So let's say we separate your body into two, one part containing the brain, liver, and kidneys, and another part containing the heart and lungs. Each part's missing organs are replaced with artificial alternatives, sufficient to keep them all alive.

Are there two living organisms? Which one are you? I say the one with the brain.

If we could split your brain, put one half in body A, the other half in body B, where is your location as a person? — NOS4A2

I don't think either would be me. I'd be dead (even if the rest of my body is kept alive by machines), and there'd be two new people (assuming that half a brain is capable of supporting a sufficient level of consciousness).

Are you identifying the brain as Michael, or just the contents of that brain? — Hanover

I'm undecided. I don't know whether consciousness is reducible to neurological activity or if it's some (non-physical?) supervenient phenomenon.

I am only explaining that a brain transplant is unlike a heart transplant. I can replace my heart with another's but I cannot replace my brain with another's.

The brain in the jar is you if it contains your thoughts, which is why a vegetative brain is no different than you arm. Your essence isn't the brain. It's what the brain happens to be storing, which means you could be you in someone else's brain or on a USB drive. — Hanover

I don't think that's quite right. There's a difference between a working clock and a broken clock, but it's not like the working clock has some additional entity that can be taken from it and added to a different clock; it's just the case that a different clock can be made to behave in the exact same type of way.

Brains are perhaps just very complicated clocks. I am a specific (living) brain. Any other brain made to behave in the exact same type of way is a different token individual.

A → B means B or not A

If I punch you then you will cry does not mean you will cry or I won't punch you.

There's no logical mistake? It's just the case that "if ... then ..." in ordinary English doesn't mean what "→" means in propositional logic.

Michael, the argument is simply this:

If it is raining then it is not raining.
Therefore, it is not raining.

Who in there right mind would conclude the conclusion from the premises in a conversational setting? — NotAristotle

They probably wouldn't, because the grammar of ordinary language does not follow the rules of propositional logic.

In propositional logic, the following is a valid argument (specifically, it's a tautology):

P → ¬P
∴ ¬P

I am referring to the "it is raining" example; the conclusion in that argument appears to be a logical leap. I get that the argument is formally valid, that's the entire point - while formally valid, the conclusion does not appear to "follow." — NotAristotle

If it is raining then it is not raining
Therefore, either it is not raining or it is not raining
Therefore, it is not raining
It is raining
Therefore, it is not raining

Or more simply:

It is not raining
It is raining
Therefore, it is not raining

Still, it also appears that the conclusion is an unwarranted logical leap from the premises, so that is why I think there might be room to argue that the argument is not valid according to some informal definition of logical validity. That is to say, the conclusion doesn't follow or doesn't lead to the conclusion. I understand that this is not the definition of validity formally speaking. — NotAristotle

The conclusion logically follows, as has been explained many times.

P → ¬P
∴ ¬P ∨ ¬P
∴ ¬P
P
∴ ¬P

Or more simply:

¬P
P
∴ ¬P

The only issue is that people misunderstand what "P → ¬P" means. It doesn't mean what "if ... then ..." means in ordinary English.

Let's suppose an non realist comes to the conclusion that there are no cups. — Sirius

Not all anti-realists claim that.

This is the sort of argument that an anti-realist might make:

P1. A cup exists if and only if there exists some X such that X is a cup
P2. For all X, X is a cup only if X is being seen or used as a cup
C1. Therefore, a cup exists only if there exists some X such that X is being seen or used as a cup

The truth of "a cup exists" (and so the existence of a cup) depends (in part) on an object being seen or used as a cup; its truth conditions are not (entirely) mind-independent.

Note that nothing here entails idealism or phenomenalism; it's perfectly consistent with physicalism and scientific realism.