And still you kick.

Even I give up after a page or two.

:roll:

Here's the Cogito:

Cogito: I think ⊃ I exist

Here is a mooted proof that I exist, from various corespondents...
1. I think ⊃ I exist. (Cogito, assumption)
2. I think. (assumption)
3. ⊢ I exist. (1.2, MPP)

This proof is not the Cogito, although it makes use of the Cogito. It does not show that the cogito is true, because it assumes the Cogito. — Banno

What fallacy did you mean?

Oh, I see - you just wanted to join in the kick fest.

...fallacy... — Lionino

What fallacy?

Here's the Cogito:

Cogito: I think ⊃ I exist

Here is a mooted proof that I exist, from various corespondents...
1. I think ⊃ I exist. (Cogito, assumption)
2. I think. (assumption)
3. ⊢ I exist. (1.2, MPP)

This proof is not the Cogito, although it makes use of the Cogito. It does not show that the cogito is true, because it assumes the Cogito.

It is a valid argument that I exist. It is not a proof of the Cogito.

Now @Corvus attempted to show that the Cogito is invalid, with the following:

1. I think ⊃ I exist. (Cogito, assumption)
2. I don't think (assumption)
3. ⊢ I don't exist. (1.2, ?)

This has the form (p⊃q, ~p) ⊃ ~q. This argument is invalid. It will remain invalid even if, as points out, everyone is entitled to their opinion. Corvus has not demonstrated that the Cogito is invalid.

Here's a seperate point, made by Corvus, Beverly and myself, and pretty much unaddressed by others: It has not been shown that the Cogito is valid.

Indeed, in propositional logic, the Cogito would be rendered
1. p ⊃ q
Which is invalid.

So, is the Cogito is a valid inference?

Yep. True, but invalid.

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

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

I now sincerely regret having become involved in this discussion.

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.

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?

So...

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

Still 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.

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.

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.

Go on, set out your reductio.

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

if I don't exist, then possibly I think. — NotAristotle

Is that what you wanted to show? That's not the cogito.

It means "get on with it".

:roll:

It is valid.

Mind your p's and q's. What are they?

Yes, I can doubt everything except that I am doubting (which already includes that I am, which is the point of cogito). — Fire Ologist

Well, it seems from the length of this thread, that one can doubt that, too.

Consider this: we know things despite not being "100% certain".

"I exist" is an inference. — flannel jesus

Ok, so from what is it to be inferred? And if the answer is "I think", then how is the inference valid?

I've set out my view. The project here, to find something indubitable, is the source of the problem. Just as we can require reasons to believe, we can require reasons to doubt.

Or not.

A better account than others have provided.

Can you doubt that you are now reading my reply?

Point being, at the level you want to work, there are quite a few things besides the Cogito that are evident.

All, can you see that the Cogito does not provide the certainty you crave?

...the idea that you wouldn't be able to think if you didn't exist? — flannel jesus

Notice the presumption in that? Consider again Russell's objection - There is thinking occurring, but what is the "I"?

The other reading, which you might be groping towards, is to take the Cogito as a definition of "I"; that "I" am the thing that thinks - well, strictly, doubts.

You insist I answer your question when you have not answered mine - inference or intuition? Admit it is an intuition, not an inference.

For one to think, one must exist. — flannel jesus

Why?

p⊃q is not a valid argument.

Move past attacking Corvus ad nauseam, we agree that he does not show the Cogito to be invalid. But can you show it to be valid?

Or is it something else? If so, what?

See

(1) If I think, then I exist. — NotAristotle

Isn't that exactly what it was you were trying to prove, NotAristotle?

Can you show that the Cogito is a valid inference? Can you set out it's logical structure, so that we can see why we ought accept it's conclusion, if we accept it's assumption?

And if not, why should we accept it?

The catchphrase is not a syllogism, the complete argument is. — Lionino

What you call "the complete argument" is obviously circular. Hardly convincing.

...the complete argument is:
Thinking → existing
I think
Therefore I exist — Lionino

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

You yourself said earlier "you must start somewhere". A start is a foundation, if you agree that we need a solid one, you side with Descartes, if you are of the side that we don't need a solid one, you are a skeptic and a pragmatist. Pick your poison. — Lionino

You are playing on "solid" here, on the he misapprehension that we can only know stuff if we are certain of it, if our belief is indubitable.

If existence is required for thought, then "I think therefore I am" makes immediate sense, don't you think? If someone agrees that "I must exist in order to think", then the cogito becomes an obvious consequence. — flannel jesus

So it's an intuition.

Is that sufficient for the foundation of knowledge? No. If someone has an intuition that folk born under Pisces are natural leaders, you'd throw it out offhand. If you want the Cogito to be the foundation of your enterprise, you will need more than intuition.

Sure, @Corvus has it wrong. That doesn't make you right.

So it must be P -> Q = Not P or Not Q — Corvus

(p→q)↔(¬p∨¬q) is invalid.

P -> Q is FALSE. — Corvus

No, it's invalid. It can still be true under some interpretation. It can also be false under some other interpretation.

But of course, that you have not shown the cogito to be invalid does not imply that it is valid. @flannel jesus has not shown that the cogito is valid - if indeed that is their supposition.

_______

The catchphrase "I think therefore I am" of course is not a proper syllogism, and it doesn't have to be, the complete argument is:
Thinking → existing
I think
Therefore I exist — Lionino

It's not a proper syllogism, yet you present it in syllogistic form? Make up your mind: is it an inference, or not?

That every single philosophical argument needs to be put in syllogistic shape is a fantasy. It is more than impressive that cogitō ergo sum, the crowning achievement of the father of modern philosophy, needs to be defended against so many bad arguments in a philosophy forum. — Lionino

Is it a valid inference, on which we must all agree, or is it an intuition, a mere hunch or impression?

_______
Underpinning the whole of this thread is the misapprehension that we can only know stuff if we are certain of it, if our belief is indubitable.

This error leads folk to conclude either that we must build our knowledge from solid foundations, such as the Cogito, or else that we do not "truly" know anything. Both views are muddled.

Obviously not sound. — Metaphyzik

:chin:

p⊃q, q⊃t ⊢ p⊃t. is the Hypothetical Syllogism.

You wrote

(I think, therefore I exist) or (I don't think, therefore I don't exist)

All your friends need do is deny the right of the disjunct - which they have done.

I simply fed what you said in the quote above into the tree proof generator, verbatim.

But go ahead and bite the hand that feeds you. I am agreeing with your more general point that the validity of the cogito is questionable - indeed, it is questionable if the cogito is an inference. Your interlocutors seem to think that it is logically undeniable. Let them show us how.

In symbolic classic logic, the contents don't matter. It works purely on the format.
So if you say,
P-> Q
Not P
Then it must be Not Q

There is no way Not P, and it is still Q. — Corvus

Corvus' argument here is of course invalid - tragic that this should need saying.

But Corvus is correct that the Cogito is not valid, at least in its usual form. "I think, therefore I am", rendered as "p⊃q", is invalid.

One needs to get inside the existential quantification if one is going to show validity. That is not an easy task.

Try it for yourself, see if you can avoid circularity.

Hence the common reading of the Cogito as an intuition rather than as an inference.

I don't think there is much point in taking up the discussion. It's too far gone.

But I insist on giving more weight to 1.1 over the first half of 2.021, misconstrued.

Consider also

2.0231 The substance of the world can only determine a form, and not any material properties. For it is only by means of propositions that material properties are represented—only by the configuration of objects that they are produced.

Facts set out the configuration of objects. Nothing can be said about objects apart from how they are configured - the facts; Attempting to say something about objects apart from their configuration is attempting to say what instead must be shown. There is nothing much that can be said about objects per se; they are instead shown in their configuration and presumed by the facts.

It has also to be understood that the Argument for Substance is rejected in PI. See especially §60-64.

In the place of some ultimate analysis of substance, or of logical atoms, or of ultimate simples, is left the various games we might play, and what we are doing in each case. What is foundational depends on the task at hand - forget about meaning, and look to use.

To understand Wittgenstein with any depth one must read the Tractatus and the PI side by side.

I'll leave you to it. But the answer to the OP is that from the perspective of the Tractatus, nothing can be said about substance or atomic objects; one can speak only of their configuration. And yes, this doesn't work, hence the Investigations.

...all muddle... — schopenhauer1

Yep. Folk hereabouts have missed Tractatus 1.1. They are trying to understand of the Tractatus as founded on objects, when it is founded on facts.

This is the worst thread so far on Wittgenstein. Quite an accomplishment.

The power of the factual is immense and prevents us from taking on other perspectives. — Wolfgang

Yep, truth keeps getting in the way.

Probability, not Certainty — Gnomon

So you are now saying Bayesian inference is only probably correct...?

To say you know something implies a commitment to something being true, and for me that implies certainty — Lionino

Good for you. If something is known, then one can conclude that it is true.

One can hardly discern whether there is something "true" about the game they just made up to communicate or whether it is a useful fiction. — Lionino

In Chess, it is true that the bishop stays on it's own colour.

I'm not at all sure we are disagreeing here.

That is to say, it would be a matter of empirical investigation to find out, both what the constituents of a thought are and how they are related to the ‘objects’ occurring in facts, that is to say, to the objects designated by the ‘names’ in language. — Summary, p. 28

What the objects are is "a matter of empirical investigation to find out", not an issue to be addressed in The Tractatus. It is irrelevant to the work at hand. As I said, what an atomic object is, as Anscombe argues, unimportant to the argument in the Tractatus as presented.

Immediately, Anscombe adds:

That this is fantastically untrue is shewn by any serious investigation into epistemology, such as Wittgenstein made in Philosophical Investigations. But it is fair to say that at the time when he wrote the Tractatus, Wittgenstein pretended that epistemology had nothing to do with the foundations of logic and the theory of meaning, with which he was concerned. The passage about the ‘elucidation’ of names, where he says that one must be ‘acquainted’ with their objects, gives him the lie. — op cit.

Now it remains unclear to me what you are claiming, but I don't much care.

If you or suppose Wittgenstein to be arguing that the world is made of objects, that objects are the fundamental building blocks in the Tractatus, you have badly misunderstood what is being argued.