Still, I would like your opinion on the conclusion, is it acceptable or not?

Banno, where are you going? I am quite sure we were just now on the verge of a breakthrough. Are we to turn away from the discussion at this critical juncture?

His central argument in this thread has been, if "I think therefore I am" is true, then it must also be true that not thinking implies not existing. — flannel jesus

I just wanted to check, is your argument here that if 'I think therefore I am' is true, then logic dictates that 'I do not think, therefore I do not exist' must also be true. But since the latter makes no sense, then something is terribly wrong with it all?? Or am I totally wrong to assume that? I could have misunderstood.

Very well Banno, I shall look to see if Socrates is around. He is usually most amenable to having a discussion.

Go on, set out your reductio.

Line 1 is invalid (edit: it is valid in S5). Again, you presume your conclusion.

Hmm, I am surprised to see that the argument is invalid and would very much like to know why it is invalid. It seemed to me to be quite a good formal argument.

But Banno, of course that argument is invalid. That argument is only 1 step. My argument is three steps. I should be quite surprised to find that the argument I laid out is invalid.

Any 1 line argument is invalid because it is not an argument! Even "If P Then Q" is invalid according to the program you referenced.

And since I really do think the argument is valid, I would ask you again whether the conclusion from my argument sounds right to you?

I just wanted to check, is your argument here that if 'I think therefore I am' is true, then logic dictates that 'I do not think, therefore I do not exist' must also be true. But since the latter makes no sense, then something is terribly wrong with it all?? Or am I totally wrong to assume that? I could have misunderstood. — Beverley

Yes, correct. You have got it spot on.

'I think therefore I am' implies 'I do not think, therefore I do not exist'. It is logically valid (reasoning via contradiction in Logic).
But I don't think or I think, therefore I do not exist is false. People do exist until death once born, whether they think or not. We know that from the fact of the reality in the world.

Therefore I think therefore I am is false. "I am" has nothing to do with "I think".
I am alive therefore I am, or I see me therefore I am are more meaningful statements.

That is a completely different objection than your "how do you know?" to something that is self-evident — Russell's objection being, by the way, mostly semantic. — Lionino

When he goes on to say “I am a thing which thinks,” he is already using uncritically the apparatus of categories handed down by scholasticism. He nowhere proves that thoughts need a thinker,nor is there reason to believe this except in a grammatical sense. — Russell, Bertrand. 1945. A History of Western Philosophy And Its Connection with Political and Social Circumstances from the Earliest Times to the Present Day. New York: Simon and Schuster, p. 567.

I was doubting your statement that nothing can think if it does not exist. Russell is saying that Descartes does not prove that thoughts need a thinker.

Any 1 line argument is invalid because it is not an argument! — NotAristotle

((p⊃q)&p)⊃q is valid, and on one line.

But if one denies p, then the argument does not bind one to q.

And I ought correct myself, or at least finesse the point; line 1 is valid in S5.

Hallelujah! I was doubting myself for a moment! I am not going mad then :)

I just wanted to check, is your argument here that if 'I think therefore I am' is true, then logic dictates that 'I do not think, therefore I do not exist' must also be true. But since the latter makes no sense, then something is terribly wrong with it all?? Or am I totally wrong to assume that? I could have misunderstood. — Beverley

Yes, correct. You have got it spot on. — Corvus

Does this make more sense to you now?

The inference is invalid. logic does not show that if 'I think therefore I am' is true, then 'I do not think, therefore I do not exist' must also be true.

Things may exist and yet not think.

That is, letting p="I think" and q="I exist", the syllogism would be
(p⊃q) ⊃ (~p⊃~q)
But this is, as has been explained many times, invalid.

The inference is invalid. logic does not show that if 'I think therefore I am' is true, then 'I do not think, therefore I do not exist' must also be true. — Banno

In the course of the proof, they are both assumptions until "I don't exist" is found False, when we checked it against the fact of human life in the world.

Hallelujah! I was doubting myself for a moment! I am not going mad then :) — Beverley

No you are not. Your reasoning and understanding are spot on.

So...

(((p⊃q) ⊃ (~p⊃~q))∧q)⊃~(p⊃q)
or
(((p⊃q)∧(¬p⊃¬q))∧q)⊃¬(p⊃q)

Still invalid.

'I think therefore I am' implies 'I do not think, therefore I do not exist'. It is logically valid.

People do exist until death once born, whether they think or not. We know that from the fact of the reality in the world.

Therefore I think therefore I am is false. "I am" has nothing to do with "I think". — Corvus

“whether they think or not”?

I thought we were on the same page but we can’t even seem to connect on what “I am” means and now you are bringing in what “I am until death once born.”

We are overthinking and adding way too much content to a simple observation - I am.

Forget the stupid syllogism.

It’s really just a simple, present moment - being here right now for instance reeding the word “reeding” spelled wrong twice now. And now reading “now.” Again!

“I am.” Is about right now, being present. Here.

Let’s drain the content. You could say “I am sitting/standing here reading now” to yourself. And whether you actually say this or believe or know anything you say or think, you already said “I am” before and during every any of them... What you say after you say “I am…” doesn’t matter anymore, it’s just content, like birth and death and think and say.

Forget the content. Whenever I say, I am saying. Whenever I think, I am thinking. The “am” is all you need to know about the cogito.

We can know that we exist, while we are existing. It’s what we do. It’s what we are doing right now, here, in this conversation. BUT, forget all that / to much content.

Words themselves do an injustice to the “am”.

This OP asks what we can know with 100% certainty. This brings in “what” and problems of identity and universal kinds.. and brings in “we can know” and problems of epistemology and its cousins physics and metaphysics… and brings in “certainty” on a scale up to 100%.

Forget all of that for one more second.

We’ve drilled down to this simple moment.

So, hey, let me ask you something.

Are you still reading?

Now let’s ask a simpler question.

Are you being?

I am.

If you are, are you sure?

I am.

This is the point in this writing where an all caps HERE makes its appearance. I typed all caps HERE
to completely waste your time.

That is where being is. Now. Currently below a couple HEREs.

That is where I am now when I say “I am.” It’s what it means to me - being in.

From this now, Descartes found certainty. That moves us away from the “am now” back into content and the stupid syllogism. I do see certainty as well, but I wonder if you even follow me here anymore.

But I don't think or I think, therefore I do not exist is false — Corvus

Corvus, is the correct interpretation here that: "I don't think...or it is false that I think therefore I do not exist." (1).

Or is the correct interpretation here: "it is false that "whether I think or I don't think I do not exist." (2).

The inference is invalid. logic does not show that if 'I think therefore I am' is true, then 'I do not think, therefore I do not exist' must also be true. — Banno

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.

Now, I may have this wrong. Maybe there is a hole in my reasoning somewhere. (Considering it is past 1am, I wouldn't be surprised, but to me, this makes sense.)

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

If A implies B then the falsity of B implies the falsity of A by modus tollens. Whereas the proposition "I do not think therefore I do not exist" must be false if indeed I do not think (and yet exist), the proposition "I think, therefore I exist" needn't be false in the event that I do not think. In that case, the falsity of the proposition "I do not think therefore I do not exist" does not imply the falsity of "I think, therefore I exist."

Corvus, perhaps you were thinking that if I did not think, I would not know that I existed; in that case, it would appear that my existing could not be decoupled from my thinking. While it is certainly true that if I weren't thinking, I would not know I existed, there is surely a possibility that I do still exist (even if I am not thinking), as Banno stated.

Banno, I am not convinced by the website/program you are citing. That program considers "If P then Q" an invalid argument, so maybe there is some problem with the way the arguments are being inputted? — NotAristotle

But p⊃q is invalid. From p it does not follow that q.

Are you sure you understand validity?

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

I follow you on the logical analysis.

Does “I am” itself mean anything, show you anything, without the syllogism and analytics?

You say it all fails. I’m wondering if anything is left at all in your view.

"If P then Q" is just a conditional operator, there is nothing not valid about it. I have never heard anyone claim that "if p then q" is not valid. Will you be claiming that p is "not valid" as well. Are you sure that you understand validity?

A formula is valid only if it is true for all assignments to its terms.

Here's the truth table for implication:


p⊃q is false for the assignment p=t and q=f; therefor it is not true for all values of its terms, therefore it is not valid.

No. An argument is valid if the conclusion necessarily follows, as a matter of deduction, from the premises. If p then q is not an argument.

I now sincerely regret having become involved in this discussion.

is p valid or invalid?

https://www.umsu.de/trees/#p

Consider the proposition "it is raining." Will you regard that proposition as valid or invalid?