Are there assignments of true and false for which it is false? Yes. Hence it is invalid.

what if it really is raining. Is the proposition still invalid?

Yep. True, but invalid.

no. You cannot jump from 'I think therefore I am' to 'I do not think, therefore I do not exist'.

In general, you cannot jump from "p implies q" to "not p implies not q".

Do you believe you can jump from "p implies q" to "not p implies not q" in general?

Do you believe you can jump from "p implies q" to "not p implies not q" in general? — flannel jesus

I believe that the following is the correct logic:

I think what he is trying to show here is that we cannot successfully use logic on the cogito in a way that it makes sense. From this, we can conclude that there is something wrong with the cogito. For example, it would obviously make no sense to say, "I do not exist, therefore I am not thinking" because you cannot be thinking about not thinking unless you exist. Or, you cannot say 'I do not exist' if you do not exist. Now, you may reply, "Oh, that was Descartes's exact point: if you are thinking, then you must exist." However, since 'I do not exist, therefore I am not thinking" DOES NOT make sense, then logically, the cogito also does not make sense. As has been pointed out many times, the 'I' is not logical here. To make it logical at a stretch (whilst having to make assumptions) we would have to change it to: 'He thinks therefore he exists.' Then, we can more logically say: 'He does not exist, therefore he is not thinking.' But, as I am sure we are all aware, the cogito ONLY works from the first person perspective. Therefore, it fails; it all fails — Beverley

He based his logic on the premise that you can jump from "p implies q" to "not p implies not q" in general. You can see him present the argument here.



He established that as the logical basis for jumping from "I think therefore I am" to "I don't think, therefore I am not."

You are agreeing with him and his reasoning, so I just want to establish unambiguously: do you think what he thinks, that for any "p implies q" type statement, "not p implies not q" must also be true? Do you agree with corvus on that one or disagree?

Does this make sense? I am just checking. Please do point out if I have made a mistake somewhere. — Beverley

Yeah you are still right. Folks seem to think still I think therefore I am is some sort of logical statement, hence all the confusions.

Because they are so confused, we were trying to show in simple classic formal logic to see whats happening there.

In the course of logical proof, regardless of being invalid or valid, we can reason by introducing contradiction to the statement, and try to eliminate or trigger truth or falsity values from the statement. At this stage every statement is assumption. Contradiction reasoning is based on the identity principle that P = P, Q = Q. Therefore if P-> Q, then Not P -> Not Q must hold. This principle is priority to being valid or invalid of the assumptions.

When we examine Not P -> Not Q, we find that statement is incorrect. Hence P -> Q cannot be true.

This has nothing to do with Not P -> Not Q is a logical leap and all that nonsense.

Cogito is a subjective intuition. No one can inspect others' cogito apart from his / her own. Hence it is not an objective concept. It shouldn't have been even started for logical process.

But you are again correct. Because Cogito is an intuition, logical proof is impossible. It can only prove that it doesn't make sense concept, hence the statement Cogito ergo sum is false.

He based his logic on the premise that you can jump from "p implies q" to "not p implies not q" in general. You can see him present the argument here. — flannel jesus

I see what you are saying, but I also see what he is saying too. I have never studied logic before, but I spent a fair few hours last night reading up on it. (So, thanks to you all, I think I may know a bit more than I did before now... I think.) I also read every one of the links you posted about modus tollens, modus ponens, affirming the consequent and denying the antecedent, hence, the position I took on, 'I do not exist, therefore I am not thinking.'

As I said, I think he was trying to show that 'I think therefore I am' does not make logical sense. I think this was his main argument there. And, for the reasons I mentioned, I agree with him. It does not make logical sense. The main premise 'I think therefore I am' is not reliable or logical in the first place to prove certainty, and therefore, pretty much anything that is said about it makes no logical sense either. (Although, of course, I cannot speak for Corvus; I can only say what I think he was trying to show. He is probably exhausted right now; he has been putting forward arguments against the cogito since page 14!) Also, I'd like to point out that this was not the only argument he gave; there are indeed other sound arguments, such as this:

Moreover, it is a circular statement. How the hell does he know that he exists? He was supposed to doubt everything. — Corvus

Descartes is indeed begging the question, or using a circular reasoning, which is invalid. Descartes assumes that he exists and then uses this to prove that he exists through 'I think therefore i am' because to think, he must exist.

This is why the logic is not working. You cannot doubt everything and then suddenly, magically be certain of something. That is not too hard to understand, in my view. It is impossible to beat the skeptics at their own game. The only way to 'beat' them is to NOT PLAY THE GAME.

This is why the logic is not working. You cannot doubt everything and then suddenly, magically be certain of something. That is not too hard to understand, in my view. It is impossible to beat the skeptics at their own game. The only way to 'beat' them is to NOT PLAY THE GAME. — Beverley

Agreed. Thinking (Psychology) ===> Existence (Ontology, Epistemology). This is a leap. It is not even a logical leap. It is a psychological or paranormal leap.

So it sounds like you're still not agreeing with what he just said, which is

Therefore if P-> Q, then Not P -> Not Q must hold. — Corvus

He's confirming it again - that denying the Antecedent is a part of his train of logic.

I want to make this clear, Beverley : I'm not overly concerned that you agree that the cogito is a bad argument. I'm concerned fundamentally with the reasoning used to get there. You said you agreed with Corvus reasoning, and this is a big part of corvus reasoning:

Therefore if P-> Q, then Not P -> Not Q must hold. — Corvus

I want to establish with you, before anything else, if this is a valid step in reasoning in your view. I'd like to be explicit about it, because if we can't get to the bottom of this, we can't get to the bottom of anything. Corvus says it's basic logic, and I agree, it's basic logic. If we can't get to the bottom of basic logic on a philosophy forum, what hope do we have to get to the bottom of anything?

And if you disagree with his logic there, that doesn't mean of course that you have to disagree with his conclusion. You can agree with his conclusion without agreeing with his reasons for getting there. If someone says "2+2 is 4 because I saw 5 guys jump Mickey mouse at Disney land", we can agree with their conclusion while still saying "your reasons for getting there are not good".

So would you mind trying to establish with me if its generally true to say "if P-> Q, then Not P -> Not Q must hold."? I would love to have this basic logic established, as it has so far been a fundamental part of Corvus reasoning to this point.

You are back! Yay! You are not collapsed in an exhausted heap trying to explain over and over why the cogito is not valid ... since page 14! Considering we are now on page 28, I'd say you have a whole lot of stamina!

So would you mind trying to establish with me if its generally true to say "if P-> Q, then Not P -> Not Q must hold."? I would love to have this basic logic established, as it has so far been a fundamental part of Corvus reasoning to this point. — flannel jesus

I have explained on the point in my previous post clearly enough.

You've explained what Beverley thinks about it?

You are back! Yay! You are not collapsed in an exhausted heap trying to explain over and over why the cogito is not valid ... since page 14! Considering we are now on page 28, I'd say you have a whole lot of stamina! — Beverley

Yes, I am bowing out from this thread after this message. I was going to do that about 10 pages ago. But I was getting frustrated to see the continuing confusions and groundless claims. It seems it better not to waste any more time, if the confusions going to continue, then let them get on with it. I don't see their views ever changing with no matter what rational explanations were given judging by their continuous circulatory posts.

Will get on with some other topics and readings. Thanks for your input on the point. :pray: :up:

I think I said enough on what I had to say. Much of them were just the repeating the ideas and points, which you seem cannot accept. I am bowing out from this thread. I have the other topics I would like to read and discuss. Thanks & all the best.

So would you mind trying to establish with me if its generally true to say "if P-> Q, then Not P -> Not Q must hold."? I would love to have this basic logic established, as it has so far been a fundamental part of Corvus reasoning to this point. — flannel jesus

As far as logic goes, the problem with Cogito is that the original premise is not a logical or valid statement. This means that you can say anything you like about it, and it still will not make sense logically. Since the original premise is not logical or valid, we are not playing by the rules of logic, so we can do or say what we like, but nothing about it will be logical. To apply modus ponens or modus tollens, or any other type of modus lol the original premise must be logical and valid...I believe. BUT I am new to all of this, so I could be wrong. There may be some 'modus' out there where the original premise doesn't need to be logical. I may not be totally read up on all my moduses!

Hold on, I should have added, IF you are playing by the rules of logic, and the original premise was valid and logical, then, if what I have read is correct, the 'not P, not Q' reasoning would not hold.

Given what you are saying here, it sounds like you are saying something different from what Corvus was saying earlier. He was using logic and what gets called a fallacy of denying the antecedent to demonstrate the cogito is false. Here you are saying that a premise in the cogito is false. That's a completely different argument and one I tend to agree with.

Yes, I am bowing out from this thread after this message. I was going to do that about 10 pages ago. But I was getting frustrated to see the continuing confusions and groundless claims. It seems it better not to waste any more time, if the confusions going to continue, then let them get on with it. I don't see their views ever changing with no matter what rational explanations were given judging by their continuous circulatory posts.

Will get on with some other topics and readings. Thanks for your input on the point. :pray: :up: — Corvus

I do not blame you at all. I would have bowed out much sooner! You lasted for pages without agreement from anyone but didn't give in. I am really impressed!

I accept that you don't agree with cogito. I'm not trying to convince you of cogito.

You have expressed agreement with corvus reasoning - there are many people on this forum who see a problem in his reasoning, but you're the only one who thinks his reasoning is good, so we can talk about it.

His reasoning is based on going from "if I think, then I exist" to "if I don't think, then I don't exist". You've read the conversation apparently, so you can see him defending this throughout the pages - am I correct about that?

So the question many of us have is, where does "if I don't think, then I don't exist actually come from?"

Corvus has provided his logic for where it comes from. Where do you think it comes from? How do you, personally, Beverley, how do you go from "if I think then I exist" to "if I don't think then I don't exist"? Or, do you go to that at all? Perhaps you don't.

Hold on, I should have added, IF you are playing by the rules of logic, and the original premise was valid and logical, then, if what I have read is correct, the 'not P, not Q' reasoning would not hold. — Beverley

I missed this the first time around. I apologize. I applaud you for reading the material on symbolic logic, even though you were unfamiliar with it, and coming to understand some operations of basic logic.

You are correct, if we are playing by the rules of logic, the 'not P, not Q' reasoning does not hold. And we ARE playinig by the rules of logic - if someone could use the rules of logic to prove the cogito entirely incorrect, then I personally would abandon it. Corvus tried to do so, but a step in his reasoning was going from 'if p then q' to 'if not p, then not q', which means that his particular line of reasoning was not the line of reasoning that would convince me to abandon it. There of course may be *another* line of reasoning, but not the one provided by Corvus.



We still don't have a single other person than Corvus who thinks that the 'Not P, then Not Q' line of reasoning is valid. We do have universities that say it's explicitly a fallacy.

I do not blame you at all. I would have bowed out much sooner! You lasted for pages without agreement from anyone but didn't give in. I am really impressed! — Beverley

Thanks :) I am not an expert in Logic myself, but it can be an interesting subject at times. I think I will reread my Logic book again to refresh the memories. But really key points here folks don't seem know are these.

1. Validity does't mean Truth. Validity of arguments means that the conclusion was derived from the premises. A conclusion can be valid, but it still can be FALSE.

2. We are not trying to find validity of the main issue here. Our aim is trying to find truth or falsity values. They seem to betting whole their lives for validity of the assumptions for some reason, and accuse for logical leap.

3. When conclusion was based on the premises and true , the argument is classed as sound. When it is not based on the premises, but true, it is an unsound argument.

4. Here we didn't need to worry about the assumptions being invalid or valid. They are still not the conclusion yet. They were still assumptions. The point was finding truth or falsity of Cogito, not validity.

5. Truth of conclusion is always checked by the external real world events, facts and the state of objects. But here "Think" being a subjective operation of an individual, it is impossible to check the truth or false value from it. But we know about the existence of humans. It exists no matter what. Once a person is born, he/she exists until death.

6. When checking a statement in Logic, introduce contradictions based on the law of identity principles, eliminate some predicates by introducing AND OR connectives with the known axioms until the main statement's truth or falsity values emerges.

I have tried present my arguments based on above points, but not many folks seem to see the points. It was frustrating at times. But you were able to see and understood them, and I am impressed too. :D Have a great day.

I do not blame you at all. I would have bowed out much sooner! You lasted for pages without agreement from anyone but didn't give in. I am really impressed! — Beverley

Are you equally impressed with flat-earthers who persist in arguing for a flat earth?

1. I think.
2. If I think, then I exist.
3. Therefore I exist.

This is my understanding of the cogito in argumentative form. Do you object to premise 1 or premise 2?

So since "it is raining" has truth table values of true and/or false then it could have been false, even though the proposition is true. Is that what you are saying?

I see your point. One would think that the parent would make sure that the clerk types in the details accurately.

One would think! Unless the parents were secret CIA operatives trying to hide the existence of the last remaining challenge to the power of the KGB in russia. You have an inheretence that Putin can't find out about, or he'll snuff out your life.

I'm *almost* certain that what's on your birth certificate is correct - I don't have any good reason to doubt it - but I'm also *almost* certain there are people in this world who are equally as sure as you are, and equally as justified, about what day they were born and, and who are *incorrect*. You probably aren't one of those people, but you could be!

I'm not suggesting you should behave as if you're not certain, of course. Don't go scream at your mom to tell you the truth of your Russian inheretence please.

Let me repeat again that I disagree with the cogito, but I think there is something you are misinterpreting about it. I think you are treating sentence order as chronology and interpreting 'therefore' as meaning causes/is prior to. When in fact if anything it means the opposite, but actually is not that kind of ontological term. It means, 'so, given that [what came before the word therefore[ is occuring that which [comes after the word 'therefore'] must also be happening

Existence comes first. Logically, and ontologically. — Corvus

This is exactly what the cogito is asserting.

Then he should have said, "I exist, therefore I think." He obviously misunderstood something.
He put the cart in front of a horse.

Sum, ergo cogito, makes sense. But it doesn't say anything new or exciting, does it?

If you do what you suggest here, you are actually arguing in favor of panpsychism. That which exists can then think.

There's a fundamental misinterpretation of what the word order of the sentence is saying about chronology and ontological necessity.

I think, therefore I am.

Does not in anyway say that thinking leads to existence or is a necessary precursor or facet of existence. If anything the opposite. But it is not focused on chronology.

And I think you are reading that sentence as indicating chronology. And again when you say.....

Existence comes first. Logically, and ontologically

You support the cogito.

And then I will reword this:
It seems to me you read the cogito as indicating via word order and the word 'therefore' that thinking is prior to existence. But that's not what the word order or 'therefore' indicates. In fact it's a misread of 'therefore.' Therefore means 'I get to conclude that something else is also true and, if anything was true before 'I think' occurred. It's not asserting this. The two processes could be simultaneous, for example. But it is not asserting precursion nor causation. And it is not saying the stuff in the beginning of the sentence causes the stuff in the second part.

Therefore could indicate that kind of chronology IF!!! there was future tense in the second part.

It is raining, therefore I will get wet (when I go out). But without 'will', it is not that kind of word.

When you reverse the cogito

I am, therefore I think.

You are actually doing what you complain about. Making existence dependent on thinking.

It indicates a process of thought not a proces of causation or chronology. The detective's thought process, not the scientists proclamation of causation and order in time.

So, again, I think you misunderstand 'therefore' and are confusing word order with a diagram of events in time.

Russell is saying that Descartes does not prove that thoughts need a thinker. — Beverley

I am aware. There is a reply to it here https://www.askphilosophers.org/question/5202 , which I find to be unsatisfying, leaving the criticism standing. The merits of Russell's criticism can and I think should be discussed, but I am afraid this thread is far from the right place to it.

Sadly, all the explanation you put forward has been given by either me or flannel before, to no avail. I ask that you spare your sanity.

You assume your conclusion in the first line of your argument. — Banno

I don't assume my conclusion in the first line because their contents are different. I am quite sure that what you are trying to say instead is that the argument has an unproven premise.

If you wanna know, Descartes talks exactly about this in his Objections and the Principles:

Screenshot is from "The Anatomy of the Soul".

It's very simple. I agree with him. You don't. I don't have a problem at all with that. I believe that everyone is entitled to their opinions. I always say that the world would be a boring place if we all agreed on everything :)

I meant to say that the rebuttal to Russell's criticism is not good, not that the criticism itself is not good, if that confused you.