But ¬(A→B), ¬B |= A is invalid. And it's not one of De Morgan's rules, which are equivalences between "^" and "v".

I say claiming that colours are "mental percepts" confines the scope to inside the brain. — creativesoul

Yep. Folk assume that colour words must refer, and that there must be a thing to which they refer, then get themselves all befuddled inventing things for them to refer to - "mental percepts" or "frequencies".

«A does not imply B» — Lionino

It's not the case that A implies B:

~(A⊃B)

Yep.

Hence forms of life are lived and shown, and cannot be incommensurable because they must all occur embedded in our activities in the world we share.

Which is another way of saying that some statements are true. And they will be true regardless of what one believes.

Hoffman makes the same mistake as Kant, supposing that there is a really, truly world out there that is different to and inaccessible from the world we live in.

But the world is the world we live in.

You may have taken his metaphorical language too literally — Gnomon

His book is titled "The case against reality"...

Spot on. So do you have an account of the reductio Hoffman uses?

Whatever, apo.

I dunno. I tried to give you an opportunity to regroup and perhaps present a case that might make sense. Instead you doubled down. Trouble is, so many of your posts evidence a strong desire to avoid serious philosophical engagement at all costs, but then every so often you make a real contribution and keep people guessing.

But that's a silly game anyone can play.

Eventually, though, one stops playing the onerous guessing game.

Here's the thing: nearly every one of your posts in this thread contains factual errors.

Somehow the neurobiology of perception has gone missing here. — apokrisis

I don't think there is any disagreement here concerning the neurobiology of perception. The issue is:

Does the color “red” exist outside of the subjective mind that conceptually designates the concept of “red?” — Mp202020

That's a question about the way the word "red" is used.

You seem to be using "experience" to mean "veridical experience". You're welcome to, but that's not what is meant when discussing Boltzmann brains. — Michael

Perhaps. If you want a word for both experiences and hallucinations you might try "sensation" or "impression". That way we can usefully distinguish between experiencing things in the world and sensations with no such connection. I supose it suits your purpose not to do so.

The Boltzmann brain thought experiment shows that such a scenario is both coherent and consistent with current scientific theories. — Michael

Then why is it contentious?

When looking at the photo of the dress, some see white and gold, some black and blue. This is a fact. What are the words "white", "gold", "black", and "blue" referring to in that sentence?

I say mental percepts. — Michael

The presumption is that "gold" is a noun, therefore there must be something for it to refer to. But there are all sorts of nouns that refer to multiple things, or do not refer at all. "Mental percept" here is quite empty - "the thing referred to by a colour word". There are colour words, and colours, because we can use them to pick out to each other different things around us. That sometimes one person sees blue where the other sees gold does not change this.

The nouns "white" and "gold" in the preceding sentence do not refer to the screen's "disposition" to emit the wavelengths of light typically associated with white and gold... — Michael

Yep.

...they refer to the types of mental percepts that I have and that those who see black and blue don't have. — Michael

Nah. When someone says the dress is blue, that is a statement about the dress, not about their mind.

It's not even a philosophical issue; it's a scientific issue. And the neuroscience shows us that visual percepts exist when there is neural activity in the visual cortex. — Michael

"Visual percepts" is again hollow. It means the patient discerned shapes. "Visual percepts" is hypostatisation.

Now you are just confabulating. That habit you have of attributing stories you made up to others.

First, this is not a derivation of RAA. It is a putative modus tollens that looks a little bit like an RAA. As I said, there are analogical similarities. — Leontiskos

What you say here is blatantly erroneous.

There is nothing "putative" about the use of MP, and the resulting schema is an instance of RAA.

..there is a measure of discontinuity between RAA and the other inferences of classical propositional logic, such that there is no straightforward derivation of RAA from these other rules of inference.* — Leontiskos

Such derivations have been presented here by several folk, including the one from the IEP given above.

You say that I have made a number of well-documented errors in this thread. — Leontiskos

And then repeated them, despite their being shown to be wrong.

* What I have said more recently is that the more purely formal a system is, the less this discontinuity of reductio ad absurdum is able to be recognized. — Leontiskos

...for someone who has failed to engage correctly with formal logic this may indeed be so.

So there will be unique and irreducible inference-axioms in any inferential system, but my claim is that RAA is uniquely unique. — Leontiskos

In axiomatic systems RAA is derived.
Go to https://www.maths.tcd.ie/~odunlain/u11602/online_notes/pdf_propos.pdf and you will find an axiomatic system. Look at proof 10.5. It is a proof of (~A→A)⊢A in an axiomatic system. Sadly, again, you are simply wrong, RAA is not "irreducible". Whatever an "inference-axiom" is - did you mean "theorem"?

So what can be redeemed here? Perhaps this might help:

...in a dialogical context (which is my primary context) a MP cannot be rebuffed, but a reductio can.
— Leontiskos
I'll invite you to set out an example. It might be helpful. — Banno

Ok. Again, it seems to be so.

Ok. I'll take your word for it.

My bad, I shouldn't have uncritically adopted your nomenclature. Laws of deduction are not usually derived from one another. But deriving equivalent schema to MT and RAA are exercises in basic logic. Here's one using MT:

ρ→(φ^~φ) (premise)
~(φ^~φ) (law of non contradiction)
:. ~ρ (modus tollens) — flannel jesus

And the conclusion is ρ→(φ^~φ)⊢~p, one of the variants of RAA.

Others have been offered.

None of what you have claimed is novel, nor hopeful.

RAA is certainly a valid inference in classical logic.

...in a dialogical context (which is my primary context) a MP cannot be rebuffed, but a reductio can. — Leontiskos

I'll invite you to set out an example. It might be helpful.

IEP gives this as the form of the reductio:
If p ⊢ ~p, then ⊢ ~p

And then

Suppose (1) p ⊢ ~p

(2) ⊢p → ~p from (1)

(3) ⊢p → (p & ~p) from (2) since p →p

(4) ⊢ ~(p & ~p) → ~p from (3) by contraposition

(5) ⊢ ~(p & ~p) by the Law of Contradiction

(6) ⊢ ~p from (4), (5) by modus ponens

@Leontiskos, is there anything in the article that corresponds to what you have been attempting to articulate?

See ( ) how what you are suggesting doesn't square with what is the case in prop logic? Deriving RAA from MT, and MT from RAA are common introductory exercises.

RAA directly leverages the LEM in an entirely unique way. — Leontiskos

Can you show this using Prop logic? If not, then why can't it be dismissed as an artefact of the limitations of Aristotelian logic?

The IEP article is surprisingly interesting.

There may be something in what you are attempting to articulate. Perhaps a difference between Aristotelian logic and prop calculus could be shown in some interesting way. But quite a few of your comments were simply demonstrably incorrect. This thread was a lost opportunity for you.

Fair enough.

I mostly ignore users who run into a thread shitting on everyone in sight who is not a mod, and that's what I largely did when Tones entered. — Leontiskos

You ignored him for twenty-odd pages?

there have been complaints about the way he comports himself — Leontiskos

Were there any that were not from you?

Seems that you cannot coherently address what he says, so you attack the man.

Leon has lost much of his credibility in this thread. You have been remarkably patient and persistent.

As a rule of thumb, if you are using physics to explain what red is, you've missed the point.

Children learn how to use the word long before they learn about atoms and frequencies.

And they use the word consistently and coherently to talk about things in the world around them. Again, how could we have agreement as to which things are red and which are not if being red were nothing more than an artifice of one's mind. That we overwhelmingly agree as to which things are red is shown by the continued use of the word. That we agree is explained by there being things in the world that we agree are red.

So red is not purely in one's mind, but also in our shared world.

Claiming red is like pain is a blunder. One does not see pain in boxes and cars and sunsets. The grammar of pain differs from that of colour

Nor does it make sense to claim red is an illusion. Colour persists and is shared.

None of which is to deny the physics of colour. The scientistic view that "there is no colour in the world" is inept, failing to recognise that humans create and maintain a shared world of language and belief.

The physics is irrelevant so long as when you ask for a red pen, that is what you are given.

So, yes, apparently brains can generate experiences in the vacuum of space. All that is required is the appropriate neural activity, regardless of what causes and maintains it. — Michael

When one has an experience, it is an experience of something. When there is no "something", it's an hallucination.

But also, that "brains can generate experiences in the vacuum of space" is a presumption, not a conclusion, of the Boltzmann brain fancy.

And finally,

Supose you are a quantum fluctuation, having just popped into existence last Tuesday. The chances of you persisting into the next few seconds are vanishingly small. Chances are the world around you is ephemeral, and will disappear, or at the least not continue in a coherent fashion.

And yet for us, the world continues on in a regular and predictable fashion.

...that the world persists shows that it is very unlikely that you are a Boltzmann brain. — Banno

Six months later, Michale is still here to argue that he is most probably a Boltzmann brain, making it vanishingly unlikely that he is correct.

Because some words pick out mental phenomena and some words don't? — Michael

But why?

...also... — Michael

In addition to what? An individuals percept and and what? A pen, perhaps?

The naive view that projects these colour percepts onto mind-independent objects is mistaken. — Michael

The naive view that denies colour to objects is mistaken. Why shouldn't a red pen simply be a pen that reflects light at various wavelengths and various intensities?

How come "pen" picks out a mind-independent object, and not just whatever has the causal role in eliciting a particular type of mental percept. Doesn't the noun "pen" refer to this type of mental percept?

Then what are you talking about? The red pen or the percept-of-red-pen? Over to you.

Me, I talk about red pens, and don't much fuss as to percepts.

No, because we're using "red" as an adjective to describe the pen. — Michael

No, because on your account we are talking not about the red pen but each of our own solipsistic percept-of-red-pens. One your account there is no red pen.

, see

Well, thank you for your erudite and productive contributions. Without you, this thread would have been much abridged.

Do (A implies B) and (A implies notB) contradict each other? — flannel jesus

Just to sum up, here's the truth table:

If they did contradict each other, the third column would all be F's.

So as things stand, 41% of folk got it wrong. Pretty sad.

Here's an actual contradiction, for comparison:

Brilliant stuff. Seems we are done here, unless you have something substantive to say?

Edit: Nice to see you have taken to quite radical edits of previous post.

Quoting only yourself might indicate a failure to address one's interlocutors. But I could make no sense of that last post anyway. Pointing out your errors has become too sad to continue. Especially if you are going to repeat things already refuted.

I'm saying that I can talk about them, just as I can talk about your thoughts even though I can't think them. — Michael

So on your account, when we agree that the pen is red, we are talking about quite different things - the percept-in-my-mind and the percept-in-your-mind.

And so on your account we have not agreed that the pen is red.

. I just deny that colours are something other than mental percepts, — Michael

Which is no more than a play on "mental".

One could conceivably learn the rules of a game without ever playing a game, which is a problem for your description. — Count Timothy von Icarus

Here's my contention:That someone is following a rule is shown by what they do.

You seem to be addressing something else - perhaps that one could not understand the rules without showing that one understands them. Not my contention.

Sure, all that can be agreed, and yet we still hold that Anellis has not carried his case.

Is it a given that Peirce didn't observe that and Wittgenstein did? — TonesInDeepFreeze

But a truth table determines validity. — TonesInDeepFreeze

Does Anellis show explicitly that Peirce used a truth table in this way? I don't see that. In the diagram on p.61 he lists some values for three terms. In the diagram on p.62, he lists the possible values for binary connectives.

Peirce’s object appears to have been to introduce matrices “partly as an aid in his classification of relations, and partly for the sake of illustrations or examples... — p.64

...not explicitly for determining the validity of any wff. Now in the absence of further evidence, it is reasonable to supose that Wittgenstein was the first to do this. What is absent is something showing that it had occurred to Peirce that the validity of a given wff can be shown by setting out it's truth table. Wittgenstein does set that out.

Now yes, it might have been that Peirce did understand this, but that is surmise.

So if you like, I overstated the case with "Wittgenstein created truth tables", but maintain that their present use has more of Wittgenstein about it than Peirce. You are welcome to differ.

I suggest it is time to move on.

The paper shows a Peirce matrix with truth values. — TonesInDeepFreeze

Sure, and that is where it seems to stop. Wittgenstein does the same thing in 5.101. Again, the novelty in the Tractatus is set out here:

4.45 For n elementary propositions there are Ln possible groups of truth-conditions. The groups of truth-conditions that are obtainable from the truth-possibilities of a given number of elementary propositions can be arranged in a series. 
4.46 Among the possible groups of truth-conditions there are two extreme cases. In one of these cases the proposition is true for all the truth-possibilities of the elementary propositions. We say that the truth-conditions are tautological. In the second case the proposition is false for all the truth-possibilities: the truth-conditions are contradictory . In the first case we call the proposition a tautology; in the second, a contradiction.

Here Wittgenstein is pointing out that we can take any "grouping"* of elementary propositions and find if it is contradictory or tautological (or neither) by constructing its truth table.

I don't see anything like this attributed to Peirce by Anellis. I'd be surprised if Peirce's logic would enable such a construct.

Curious.

A side line - I'm finding Google increasingly useless at searching for minutia of late. Any subtlety gets lost in irrelevancies.

* - a wff.

Yeah, I can see that last, but what is actually quoted in the literature from Pierce seems to be about listing permutations of Boolean operators rather than showing truth. I dunno. Just unconvinced. Whereas the quote from Wittgenstein is pretty unequivocal. My prejudice is showing, of course.

I wonder if there is a "deductive system" using truth tables - say a proof of the completeness and consistency of prop logic using only truth tables... Someone must have done it. Might have a look around.

But again,

...complete... — TonesInDeepFreeze

I'll maintain that the cardinal step, to using truth tables as a device for determining tautology and contradiction, was taken by Witti.

Meanwhile, may I take it that the point is made about tautologies? — TonesInDeepFreeze

Yep.

...anticipated... — TonesInDeepFreeze

Yep.