Yeah, who said we're small!?!

Again, he has no clue what he is talking about, ever. — Lionino

Yeah I agree with that, but if you want to show him that you probably have to agree on an example to talk about first. You don't like the one he gave, which I understand, it's genuinely a very strange example.

He previously said "if I'm swimming, then I'm wet". I think that's a fantastic example of implication to look at.

I really want to see you answer Corvus scenario about the red lights. I'll post his scenario again.

If red light, then drive away. R -> D
If not red light, then don't drive away. Not R -> Not D is False

https://thephilosophyforum.com/discussion/comment/892642

You can interpret this as "the law says"

The law says if the light is red, you must drive away.
It's false that the law says, if the light is not red, you must not drive away.

hey! Who's been driving my car!?

One can discover that they are bad at reasoning by bumping up against contradictions in their own thinking. — Leontiskos

It seems as though, with our one example of this situation on this forum, one has to be willing to see contradictions before one is able to see contradictions. Our one test example on the forum, when faced with the contradiction, can just will themselves out of seeing it

I am not trying to get out from anything like some of the senseless folks try to make out here. — Corvus

You never posted those pages from your textbook, so...

Well, I don't know what he is saying either — Lionino

I'm just giving you a way to interpret it that leaves it as a logical implication still. It's of course a poor example anyway. Just giving him the benefit of the doubt

Here's a fun syllogism in the style that Corvus likes:

If he could find that denying the Antecedent is valid in his textbook, then it's true that it's valid.
He couldn't find it in his textbook.
Therefore
it's not true that it's valid.

then interpret it as an order, that's fine.

If it's red, then the order is to drive away.

If it's not red, then the order is to not drive away, apparently

i don't know if he's saying that's a second, separate order or if he's saying that follows from the first order. Obviously to most people here (all except one), it doesn't follow from the first. You can order them to drive away if it's red and not order anything at all if it's not red, there's nothing wrong with that.

He's still just searching for new ways to deny the Antecedent. No idea why, he knows he didn't find it in his textbook.

I mean, even in English, "therefore" has most of the same meanings. As a consequnce, in conclusion, etc. It's totally understandable to go to the original French, but it really ought not to matter - we know what "therefore" means in English (by "we" I mean apparently everyone except Corvus), and it clearly includes the definition about introducing a logical conclusion.

https://www.vocabulary.com/dictionary/therefore#:~:text=(used%20to%20introduce%20a%20logical,reason%20or%20as%20a%20result

The guy has a narrow understanding of a word in a language that isn't his first language, which is understandable and I don't fault him for that - the part that isn't understandable, that I do fault him for, is that he has absolutely 0 humility about it. He refuses to hear, from native English speakers, that "therefore" has different uses than what he insists it must mean.

The whole ordeal is a never ending illustration of the Dunning Kruger Effect

Yes thanks for the correction. — Metaphyzik

Yes no problem. I think your intuition was leading you in the right direction anyway, which is a good sign. Good logical intuition is valuable, because if you don't have it, your intuition leads you to thinking absurdities like "if it rained, the ground is wet; it didn't rain, therefore the ground isn't wet".

Have you tried reading his posts over and over again until you agree with him though? That's his recommendation.

not exactly, but almost, sort of.

If you analyse the truth table of ~(p implies q) , it's only true when p is true and q is false.

Which is the same truth table, not as (p implies not q), BUT (p implies not q) and (p). So I think you're half right, but you need that "and p" to complete it.

https://www.umsu.de/trees/#(~3(p~5q))~5((p~5~3q)~1p)

Of course the frustrating part is, in natural language when someone says "it's not true that p implies q", they're not actually saying "p and not q", they're usually saying "p and q don't have that relationship, maybe no relationship at all".

Like if someone says "You're a virgo, that means you have a small brain", and you say "that doesn't imply that", you're not saying it means you're a virgo and you DON'T have a small brain, you're saying there's just no relationship between those two variables. Classic logic doesn't capture that well, it seems to me.

This is one of those instances where it's clear that natural language reasoning can diverge from symbolic logic.

I actually think it's a great opportunity. What we have here is someone who is *perfectly* wrong - I dare say there's very few things that are more provable on this forum, very few debates that are more explicitly settlable, then "Does P implies Q mean notP implies notQ?" Corvus APPARENTLY believes in logic, he's not in here saying "logic isn't useful / logic doesn't make sense / logic is a government trick", he believes in logic, he's just completely wrong about it.

Which makes it a fantastic little experiment, I think. Can you use logic to prove to someone that they've lost their grasp on logic? I think that's a wonderful question. No better opportunity to test it than here.

you're right, I should. Crunch crunch

He thinks implication is equivalence, it seems — Banno

Yes, that's what I was getting it when I was comparing it to a <-> b.

If all instances of implication p->q also mean notp -> notq, then all p->q are really p <-> q.

Which is kinda broadly similar to equivalence, I suppose.

If it rains, then the ground is wet.
It doesn't rain.
Hence the ground is not wet. — Corvus

In Corvus world, there's only one way for the ground to get wet. That's the absurdity of taking p->q to imply notp -> notq - everything can only happen in one way, every property can only exist in one thing.

If you're arnold schwartzanegger, then your muscles are big.
You're not arnold schwartzanegger.
Therefore your muscles aren't big.

It's a hilarious type of reasoning really.

you'd have to convince him to first. He thinks that's Modus Ponens, and then insults people who look for sources about modus ponens to show that it's not.

is Descartes arguing about something so urgent? It doesn't feel urgent like that to me. I agree with the cogito, but someone like banno saying he isn't certain of it... I don't think banno is making an urgently dangerous error or anything (maybe no error at all). Do you?

Whatever consciousness is must be "casual" in some sense, I totally agree.

if denying the Antecedent were valid, you could just prove it. You want to find these goofy exits to these conversations because you want to maintain your own denial.

wait wait wait, you can be as insulting as you like, but if I say I don't like you slinging shit, I'm at fault because I used a naughty word?

Dude, just don't sling shit. Naughty words are fine. Unnecessary shit slinging is not. This isn't preschool, people can say naughty words.

You always find the goofiest ways to cop out of defending your arguments , never a real defense. The latest cop out: my mom told me not to talk to people who say the s word.

My point is clear, here's my non shit slinging point:

You cannot logically go straight from p -> q to not p -> not q. If you're in a situation where p implies q, that does NOT mean you're necessarily in a situation where not p implies not q. That's why denying the Antecedent is a formal Fallacy

Your arguments so far amount to applying that Fallacy

yes, please tell me the point without saying things like

You seem to have read something about MP on the internet and been parroting about it

Can you get to the point without slinging shit?

Do you want to just sling shit or do you want to defend your use of modus ponens? I could waste your time talking about how you parrot nonsense until cows come home, or we can talk logic. You ready to stop slinging shit and talk logic?

Insisting that denying the Antecedent is something you can do because of modus ponens is absolutely like that. You ready to talk about it or what?

Yes, you can explain 2+2 = 5 many many times and still be wrong. Most of your explanations involve saying some nonsense about "logic can't involve content" and other non sequiturs. In other words, non-arguments to prove a Fallacy. Usually followed by a complete unwillingness to investigate your own logic seriously.

Right, so once again, unwilling to actually use logic to defend a point, read my posts over and over again until you agree with me, yada yada. Tale as old as time. Can't wait until you're actually ready to start looking at logic.

You just said some random goofiness followed by an insult. Where's the logic ?

I'm gonna go out on a limb here and say he probably doesn't agree with your reasoning there because (p implies q) implies (not p implies not q) is not generally true - it's called Denying the Antecedent, and you can't just do that to any ol argument. There are some arguments you can do it for, but it's not generally applicable to all (p implies q) premises.

He's asleep I believe, so he can answer you himself later

I'm just saying, the bit about a <-> b is directed at me, not at you.

he was replying to me, not to you. He was asking me to prove something. He quoted you so I appreciate why you would think he was asking you.

those two quotes are about different things. Goodnight

I don't think it's trivial. It means denying the Antecedent, if applied as a universal rule, has genuinely absurd consequences.

That doesn't mean much, you can just have the right side on it's own and it's already valid.

https://www.umsu.de/trees/#(t~4e)~5(t~5e)

I'm not sure what you're getting at with that.

Yes, I slightly misstated the argument, as I said.

(t→e)→(¬t→¬e) isn't itself equivalent to (t↔e), it's equivalent to saying "if you have an implicaation (t→e), it's safe to say (t↔e)". He's turning ALL implications into bidirectional implications. Which has some absurd consequences.

https://www.umsu.de/trees/#((t~5e)~5(~3t~5~3e))~5((t~5e)~5(t~4e))

I slightly misstated the argument. If (t→e)→(¬t→¬e) holds, as a general rule, then all (t→e) are actually (t↔e).

any time you have (t→e) and (¬t→¬e), you have (t↔e).
https://www.umsu.de/trees/#((t~5e)~1(~3t~5~3e))~5(t~4e)

I can prove it

that he is wrong does not imply that therefore the Cogito is valid. — Banno

I don't think anybody has that train of thought

The premise is invalid. But it is not a contradiction. That is, it seems possible. — Banno

Of course it's possible, it's equivalent to saying a <-> b, and there's many a and b for which that's true.

But the cogito doesn't say a <-> b, it just says a -> b.

So how is Corvus turning a -> b into (a -> b) -> (not a implies not b)? We already know, because he told us. He says any logic textbook will show, modus ponens means you can deny the Antecedent.