Here's what the real modus ponens looks like in the checker

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

That's affirming the Antecedent, which is how modus ponens really works.

Then we modify it to your denying the Antecedent variation

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

Invalid

I can be certain about my date and place of birth from my birth certificate. It's a legal document that requires the signing off by the parent and the midwife.

if we're loose about what we mean by "certain" and don't mean "exactly 100% certain" then totally.

But if certain means perfectly 100% certain, no room for error, then it just seems immensely easy to think of things that could go wrong. One of my ex girlfriends had her middle name misspelled in her certificate - swapped a g for a j. If that's capable of happening, I find it very easy to imagine someone writing in a wrong date, swapping a 6 for a 5 perhaps.

And that's not even getting into the conspiratorial stuff.

If you feel certain, all the power to you. I just don't think so. I don't think it's fair to say, about this sort of thing, "there's absolutely no way anything on my birth certificate could be incorrect".

Do you agree with him for the same reasons he thinks? — flannel jesus

Not for the same reasons.

He thinks that if someone accepts "I think therefore I am", they must also accept "I don't think, therefore I am not". — flannel jesus

I disagree with that.

My point is that it is tautology, not that it is unsound or invalid. Saying “I think therefore I am” to yourself does show a logic only to yourself. You, the existing one (as premise), thinking or saying or being, to conclude “I am” - it’s not bad logic, it just just a tautology that doesn’t tell you anything you didn’t already know.

“I do not think, therefore I am not” doesn’t work here. (Except for maybe Parmenides.). If you assert anything whatsoever, you already are, so you can’t conclude from it “…therefore I am not”. The act of asserting even “I do not..” is an act of “am being”. “I negate, therefore I am” makes it a positive assertion that shows the conclusion “therefore I am not” to be unsound. This is why Descartes couldn’t doubt anymore. This is why he found his certainty. Undoing the logic of the statement “I think therefore I am” can never lead you to doubt the fact that you are.

To the extent it is an argument, it is still self-validating (to yourself when you say “I am”).

I think, therefore I am (which Descartes barely actually said) is the catchphrase for “Knowing something to any degree of certainty, or just thinking about something, requires an act of being, or is itself an act of being, therefore, I can know with 100% certainty that I am being, when I am thinking or when I am knowing something else with any degree of certainty.” And this tautology laden argument validates itself when it is a thought, or when you say it out loud.

Someone who speaks and who has the ability to hear at the same time: You don’t need to wait for your own words to reach your own ears to already know the listener exists; no logic need bring you to this conclusion. The listener exists because the listener is the speaker who made the noise.

Bottom line to me, “I am” can only be a premise. It’s an ontological observation, not a logical conclusion (except to yourself if you were ever wondering who that was who was doing all that thinking inside your head).

I disagree with that. — Fire Ologist

Interesting.

He has told me that I'm incapable of understanding basic logic because I don't think (p implies q) implies (not p implies not q). I of course do not think that that means I don't understand basic logic, and I can't find a single source that agrees with him on that - and I've looked. He has looked to, and has come up short.

To the contrary, I think it's basic logic that you can't just jump from (p implies q) to (not p implies not q). I can find quite a lot of sources that agree with me on that.

Let them show us how. — Banno

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. — Banno

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

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.

Your formula seems incorrect. This is the correct one. — Corvus

That means nothing in this context. You can change it to https://www.umsu.de/trees/#(p~5q)~2(p~5~3q) or https://www.umsu.de/trees/#(p~5q)~2(~3p~5q) and it remains valid.

I agree cogito is not a logical statement, and it looks doubtful if it is even an inference. — Corvus

That was never your argument.

(P -> Q) = -P or Q (P. Bogart) — Corvus

Curious, you were just saying how Bogart is not god. In any case, I already proved how this is in full agreement with Descartes:

I think → I am. P is "I think" and Q is "I am".
P – Q – ¬P∨Q (aka P→Q)
0 – 0 – 1 "I don't think and I am not" holds P → Q
1 – 0 – 0 "I think and I am not" does not hold P → Q
0 – 1 – 1 "I don't think and I am" holds P → Q
1 – 1 – 1 "I think and I am" holds P→Q — Lionino

It seems that compared to the OP, he is malfunctioning, as then he clearly understood the problem of skepticism, but now he seems to think that it is a complete logical impossibility that he is adopted or that he got switched up in the hospital.

You, the existing one (as premise), thinking or saying or being, to conclude “I am” - it’s not bad logic, it just just a tautology that doesn’t tell you anything you didn’t already know. — Fire Ologist

It seems tautological because it is so obvious, and it is obvious to us now because he pointed out, but he did have to point it out.

It seems tautological because it is so obvious, and it is obvious to us now because he pointed out, but he did have to point it out. — Lionino

It’s a tiny bit of logic as a statement, but it is a monumental basis for science. Things we may know can be demonstrably proven true, and valid and sound because, for example, “I think, therefore I am.”

That means nothing in this context. You can change it to https://www.umsu.de/trees/#(p~5q)~2(p~5~3q) or https://www.umsu.de/trees/#(p~5q)~2(~3p~5q) and it remains valid. — Lionino

Of course it is valid. Hence the assumption, Not P -> Not Q is valid. That was all it was trying to present. You too, seems not knowing the difference between validity and truth. Something is valid doesn't mean it is also true.

Curious, you were just saying how Bogart is not god. In any case, I already proved how this is in full agreement with Descartes: — Lionino

I never said Bogart was no good. I said Bogart was not a god. You seem to keep distorting the facts habitually. His point can be taken where it proves my point in the argument, but Bogart is not a god, and he is not no good. I don't know he is good or not good, and I know he is not a god.

Thinking → existing
I think
Therefore I exist — Lionino

There is no logical ground to deduce Thinking -> Exisiting.
I think therefore I exist is nonsense.

As I said before, Logic can only show you if the arguments and conclusions are derived from the premises. It cannot tell you the propositions themselves are true or false. You must get the truths or falsity from the real objects, situations and events in the world.

Cogito cannot be examined for truths. Therefore it is a meaningless statement, and Cogito ergo sum is a false statement based on the meaningless premise.

Cogito cannot be examined for truths. Therefore it is a meaningless statement, and Cogito ergo sum is a false statement based on the meaningless premise. — Corvus

That is too sweeping a statement. It’s not meaningless. It’s something kid can derive meaning from.

It’s not possible for you to think you are while you are not. That is a positive assertion about objective reality (to yourself).

There are moving parts with content. Thinking is objective content. It’s an instance of general being sought as a ground for something to know. Knowing is part of the content. The general “being” versus the particular “thinking” is part of the content (happens to be in the premise and the conclusion turning this into tautology, but there are distinctions). And because there are parts there is a logic that stitches them into a single, somewhat tautologous, meaningful and certainly true statement.

Thinking is objective content. It’s an instance of general being sought as a ground for something to know. — Fire Ologist

Thinking is a subjective mental activity. Content of thinking is private with no access possibility to other minds. To the owner of the mind, thinking is realistic. But to the rest of the world, thinking mind of you is an unknown entity. Until you demonstrated your thought contents with your actions or linguistic expressions, your thinking has no existence apart from to your own mind.

Even if you have demonstrated your thoughts publicly indirectly using your actions and linguistic expressions, the other minds wouldn't have 100% direct knowledge of your thought contents.

Therefore I think therefore I am is a meaningless statement to the rest of the world, and it is not an objective statement.

I see me therefore I am, would be a more meaningful statement. Because at least someone else could verify your existence visually against your statement.

Therefore I think therefore I am is meaningless statement to the rest of the world, and it is not an objective statement. — Corvus

Completely agree the statement "I think, therefore I am" demonstrates nothing objective to you about me. But "I think therefore I am" or better put, "thinking 'I am'" to myself demonstrates the objective fact of thinking as content in the world. The world is just very small, objectively comprised of me thinking "I am."

I have to assume there are other thinking beings, but I don't have to assume that if a being is thinking, it is being. I can know this with certainty because thinking is already a particular instance of being.

I am uncertain of everything (even myself existing), and even nothing since nothing requires understanding of what is not nothing to compare by, like knowing where a hole in the ground is by understanding where a hole in the ground is not. It could be that people actually know things, but it could be that they don't. But despite myself being uncertain of everything and nothing, I have faith in logic, science, etc. which is why I'm able to type up this response right now. Life doesn't have to make sense, we just want it to, this is why everything requires faith.

The positive point in understanding that everything requires faith has to do with why I have faith in the first place, which is believed positive benefit. This opens up a gateway of having faith in other things for believed positive benefit. Many people think they can know things, so they don't think they desire to have faith in things (after all, if they know things, why would they do something as uncertain as having faith?). I've seen many who (in my opinion) are basically weakening themselves by thinking this way, by being unable to admit how uncertain they are of life they are unable to have hope to the degree of what I see as being healthy.

Therefore I think therefore I am is a meaningless statement to the rest of the world — Corvus

This is the second time you've made it out like it's about other people - it's about yourself, not others.

It's "I think therefore I am", not "he thinks therefore he is".

https://en.m.wikipedia.org/wiki/Cogito,_ergo_sum

Descartes's statement became a fundamental element of Western philosophy, as it purported to provide a certain foundation for knowledge in the face of radical doubt. While other knowledge could be a figment of imagination, deception, or mistake, Descartes asserted that the very act of doubting one's own existence served—at minimum—as proof of the reality of one's own mind

Look at that last sentence - twice, it says "one's own". One's own existence, one's own mind. "I think therefore I am" is a statement for the speaker of that statement to understand as it pertains to himself, not to understand about someone else.

Your disagreements thus far have all been based on misunderstandings, misunderstandings of what the argument itself is about, and misunderstandings of basic logic like modus ponens.

But "I think therefore I am" or better put, "thinking 'I am'" to myself demonstrates the objective fact of thinking as content in the world. The world is just very small, objectively comprised of me thinking "I am." — Fire Ologist

This is true. It is real to you, but it is nothing to me. Likewise, you would never know what I am thinking. It is true and real to me, but nothing to you. Therefore it is why, I think therefore I am is a subjective statement. It is a psychological mumbling or monologue, or as Banno put it correctly, an intuition to oneself.

When someone said, I think therefore I am, it doesn't mean a thing to me. I can only presume, that the person is making some mumbling noise to himself.

I exist, because I see me visually, hear me talking to the other people, and they talk back to me in reasonable manner and interacting with the world as per cause and effect principles, not because I think I am.

I know X exists, because I can see it, touch it and feel it. Not because I think it exists.

It is a psychological mumbling or monologue, or as Banno put it correctly, an intuition. — Corvus

No, it's discovery of a certain objective fact in reality. It's just a discovery each has to make all by themselves. It doesn't mean nothing is discovered, or nothing is - quite the opposite.

What you are thinking is irrelevant. If you are thinking, you are - that's the whole point. That's it.

Descartes was doubting. Do the objects of sense exist? Maybe not. Does his body exist? Maybe not. After removing everything that could be removed he was left with "I am".

This was his very first premise. The confusion here is that "I am" is not a logical conclusion, it's a discovery of a first premise, one that, because of it's objectivity and certainty, can be used to build the first bit of knowledge about the world "I am in it" or "the world is at least my thinking."

Descartes didn't conclude from logic that he exists; he used logic to conclude that everything else might not exist. Then he was left at a moment where there was this thing he could not doubt. That was his first premise.

To make this a bumper sticker moment, we coined "I think, therefore I am." Which axiomizes the premise. Now we have a source of meaning, content, truth, certainty. Tons to work with. Finally after all of that doubt.

So in a sense I agree with you that the syllogism "I think, therefore I am" is really not a good example of syllogism, as it is really a colorful way of saying "I am, therefore I am" which merely clouds the premise "I am" (which is certain throughout this exercise) in a conclusion.

So in a sense I agree with you that the syllogism "I think, therefore I am" is really not a good example of syllogism — Fire Ologist

We seem in agreement there even if not in complete degree. Well, that's a progress suppose.
Thank you for your input on the point.

There is no logical ground to deduce Thinking -> Exisiting — Corvus

It doesn't need a logical ground. Nothing can think if it doesn't exist. Your criticism changes with every post you make. But it is always a stupid criticism.

You too, seems not knowing the difference between validity and truth. Something is valid doesn't mean it is also true. — Corvus

What a clown. Goodbye.

It doesn't need a logical ground — Lionino

Even if it did, he's already agreed with it prior in the thread. He agreed that someone has to exist in order to think. He just doesn't understand how that means "thinking -> existing".

You too, seems not knowing the difference between validity and truth. Something is valid doesn't mean it is also true.
— Corvus

What a clown. Goodbye. — Lionino

Suppose this is a typical response when the hidden ignorance was revealed. :nerd:

What a clown. Goodbye.
— Lionino

Suppose this is a typical response when the hidden ignorance was revealed. :nerd: — Corvus

Really guys - we are at the root of any certainty, any practical use for logic at all - that is the subject.

There is a practical, raw observation at play here, namely “I am”. This shows what certain knowledge looks like. This is a whole universe to enter (may be a small universe - Descartes immediately had to toss in God to find anything else.). Shows how a mind that developed mathematics and modern science would want to move, on certain, empirically verifiable ground.

Then there is the logic built around and on top of it “I am.” This logic “I think, therefore I am” is not great logic; it’s not a syllogism tempered for the rigors of analytics.

But Descartes was still a genius. His discovery in “I am” will forever be a part of philosophy. So downplaying the cogito as meaningless nonsense is just missing the point.

What other philosophical assertion besides “I think, therefore I am” joins the objective physical reality of my experience with my subjective reality of experiencing anything? When I experience anything, because of Descartes, I can admit things exist. It gets you out of your head by placing you in the world with certainty. “I think over here in my head, therefore, it’s already true that something is there in the world.”

You too, seems not knowing the difference between validity and truth. Something is valid doesn't mean it is also true.
— Corvus

What a clown. Goodbye.
— Lionino

Suppose this is a typical response when the hidden ignorance was revealed. :nerd: — Corvus

People often resort to name calling if they are unable to find a way to respond to someone's comments.

I have to say, your patience at trying to get your point across is admirable. I don't think I would have so much patience. I would more likely think, "Let them just believe what they want."

What you are saying always seemed so clear to me, even before I researched how other philosophers criticized Descartes's cogito, I had already come up with similar ideas.

Nothing can think if it doesn't exist. — Lionino

The thought that immediately sprang to my mind was, "How do you know?"

(Before someone points out that I had a thought, so I must exist, just take it that I am not really here typing this, and you are not really there reading it, just to humour me ;) )

Descartes’s indubitable facts are his own thoughts—using “thought” in the widest possible sense. “I think” is his ultimate premiss. Here the word “I” is really illegitimate; he ought to state his ultimate premiss in the form “there are thoughts.” The word “I” is grammatically convenient, but does not describe a datum. 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.

What you are saying always seemed so clear to me — Beverley

All of what he's been saying? Including his reasons for disagreeing with the cogito?

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.

In other words, (p implies q) necessitates (not p implies not q).

Do you think this is good reasoning? For all p implies q, must it also be true that not p implies not q?

People often resort to name calling if they are unable to find a way to respond to someone's comments.

I have to say, your patience at trying to get your point across is admirable. I don't think I would have so much patience. I would more likely think, "Let them just believe what they want."

What you are saying always seemed so clear to me, even before I researched how other philosophers criticized Descartes's cogito, I had already come up with similar ideas. — Beverley

Great minds think alike. Fully agreed with your fair and accurate analysis and comment on the point. :cool: :up:

Don't pat yourself on the back too hard. True patience would actually involve *considering what the people you're talking to say*. You haven't begun to do that yet.

Before someone points out that I had a thought, so I must exist, just take it that I am not really here typing this, and you are not really there reading it, just to humour me ;) ) — Beverley

Can’t humor you there. It’s not possible that both you do not really think you are typing this and I don’t really think I am reading this; at least one of us (certainly me) is having the phenomenal experience of at least one of these two scenarios (namely me reading). You could be doubting you were typing, and I could be doubting I was reading, but neither of us could conclude to ourselves that means “I might not exist” while doubting, while reading, or while typing.

You said “I just take it that I’m not really…”. You said “I” twice here to make your point (in type I take it.) So you demonstrated the certainty to yourself that “I take it, therefore I am” really whether you want to admit it or not. You can’t experience yourself not experiencing yourself. If you take anything, taking, or being, has to be taken with it.

I would think the next line of reasoning would be to explore the certainty outside of tautology.

Assuming you aren’t arguing from a solipsistic point of view (a useful endeavour sometimes but gotta pick your moments) there are things all of us are certain about. And to quantify that we need something fairly universal to act as a substrate for a pattern (or just cut it up by psychology like Quine, or whatever division you happen to like at the time).

I’ve always like the idea of division not by psychology or language / semantic distinction - but by the state of change in a facticity. Aka dynamic or static. Doing so leads to consider how we can learn things, and probably it is only by dynamic events that we learn anything. Certainly (pun intended) we can’t know anything about something that doesn’t change. At least that is one line of reasoning. Or a boundary that isn’t semantic or psychological. What other boundaries are worth considering?

What are the benefits and drawbacks of these boundary positions (Quine, Wittgenstein, Descartes, etc etc etc) that have already been proposed and why do we think those are the only ones to consider? Aka is everything else already a subset of a semantic argument (probably)….

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.

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. — Banno

In my conversation with Corvus, he himself has already agreed with the necessary intuition to agree with the Cogito - he has agreed that existence is required for thought.

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.

I'm not trying to prove it to everyone, generally - mainly, I'm just pointing out that this guy's counter arguments do not hold. His main one is an explicit formal fallacy, denying the antecedent. It's a fallacy EVEN IF the cogito is incorrect - his conclusion being right or wrong is independent from his reasoning being explicitly wrong. The conclusion is of less interest to me than the reasoning used to get there.

People often resort to name calling if they are unable to find a way to respond to someone's comments. — Beverley

It gets frustrating to teach multiplication to those that don't understand addition.

he thought that immediately sprang to my mind was, "How do you know?" — Beverley

Which is not Corvus' objection, as he himself does not know what his objection is.

The thought that immediately sprang to my mind was, "How do you know?" — Beverley

And the thought that sprang to mine is "Show how it could be otherwise". You are not playing the ultimate skeptic game well.

Here the word “I” is really illegitimate; he ought to state his ultimate premiss in the form “there are thoughts.” — 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.

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.

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

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

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

It is a valid inference as I have shown. As to the others, I am not sure what you mean by them, and my brain is too fried today to try to reply.

This error leads folk to conclude either that we must build our knowledge from solid foundations — Banno

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.