I don't think we exist much beyond our subjective understanding/feeling/cartesian understanding of ourselves. Outside of that, what is to say?

I just ate some kielbasa.

Because you know you'll die.

That's a good one. It gives me a true sense of confidence about my (temporary) existence.

Existential dread may also be how we know we exist. It being at the center of the human condition.

Indeed: my existential terror is an old familiar friend. When it comes around, I welcome it in, get close up and personal with it. I am not longer afraid of pondering the stuff that terrifies me the most: people commiting evil and injustice, bad parenting, human traffikers, global warming, road kill, etc. When they come around, I mourn them as I ruminate on them one more time, and at some point they go away and leave me in peace for a while.

For me, one great thing about ageing is getting more comfortable with the utter abandonment that I feel at times. I kind of revel in the fact that I've learned how to do that.

I've been listening lately to Bowie's last album--especially Lazarus and Blackstar, and I find it so comforting how he made beautiful art out of dying. Bowie was sublime, and so is anxiety, in a way...

Cogito ergo sum.

But I can only prove that with any 100% certainty to myself, not to you.

How would having a proof help you or me?
I am pretty sure of the proof claiming the diagonal of a rectangle is a certain value. I use it all the time with no problems coming up so far.
I don't understand the doubting of existence thing. I have a lot of problems but none of them look like that. I just don't get it.

'The self' does not 'exist' for much of the time! It is evoked by social and physical interactions like the convening of a committee as required. Like all concepts, 'selves', 'rocks', gods'...etc, its status as an entity rests on its transient relationship with other conepts which are coined by socially acquired 'words'. What we tend to confuse is 'self as as an actor amongst others' with 'self awareness'. The first is assigned relative permanence like 'rocks', but the second comes and goes. If in doubt, consider where that awareness goes during sleep, or when engaged in 'automatic' movement or driving a car.
These issues are discussed by Heidegger with his conept of Dasein, and by nonrepresentationalist language philosophers like Quine, who argue that the meaning of any word (like 'self' or 'existence') has no absolute value but depends on the context in which it is used.

I don’t know, I doubt. Generally parallel to Descartes, ‘I think ...’ as ‘I doubt...’

Not trying to be clever by saying that. If I knew anything in some universally applicable sense then I would know everything and be nothing - they’d be no room for relation via doubt. As I can question my existence I understand I am necessarily limited, or I wouldn’t be able to ‘understand’: I wouldn’t be able to ‘think’.

It is maybe more tricky to grasp what I am saying than I personally believe because generally ‘knowing’ is not regarded as some ‘absolute-knowing’ in the manner I’ve framed it. I’d also add though that by the manner in which you’ve framed you question you’re actually framing the meaning-use of ‘knowing’ in precisely the same way.

The universe exists because it cannot fully be fathomed. Consciousness exists because it cannot fully be fathomed. Items of imagination exist because they’re abstracted from something - experience/s - that cannot fully be fathomed. Yet we use the term ‘knowing’ in more day-to-day sense as a system of navigation (recognition, communication and efficiency seeking).

This is not a relativistic position! Doubting doesn’t mean I avoid sustenance, self-preservation and exploration.

If I could prove the relative physicalistic existence of my being (exist, as the general natural world) no one would understand it and I’d no longer ‘exist’. It’s more about the question being limited in it’s range and assuming it means something ‘beyond’ comprehension.

I found Kant the most clinical in this investigation of ‘existing’ - although it was never his direct attention to address this apparent question. Heidegger is also quite interesting (even if he’s more evasive than precise, he at least presents some nice perspectives from which to view the epistemic/ontic problems). Also, Husserl is another who flits on the fringes of this topic - much like Kant. But Husserl is more concerned with ‘bracketing out’ such questioning in order to delve more readily into the machinations (an indirect, and disinterested, approach: something in common with Kant even if their overarching approaches differ dramatically!).

That’ll do! I tried to be precise and succinct enough not to cause a headache (probably failed) :D

Also bear in mind, at the back of your mind, that any certainty about really "existing" (i.e. self-existence) might be less certain than we think. We might, after all, be nothing more than non-existents.

What reason is there to doubt that I exist? Indeed, how could such a doubt be coherently proposed?

Banno. The reason to doubt your existence is a consequence of the difficulty to proof your existence. Even old Descartes felt this to be a prerequisite for going anywhere - only after achieving this "certainty" was he ready for "conquering" greater things.

It doesn't really matter if you exist or don't exist. It won't change anything

Depends on what you mean by "know" and "exist".

For the first part, to me, knowing is acting modulo reasoning. For a pragmatic treatment (i.e. not spiritual one), reasoning is means to an end. It isn't there for your fulfillment. You know that you exist as much as you know that the stove is hot. In some sense, you don't. But acting like the stove is cold has consequences, and you choose knowledge as the opposite is not feasible. You are specific and in specific circumstances, and in no position to bail out from the present. You are already involved, and as a result you have to think in correspondence with the situation. Existence was there before you, and now you have to come to terms with it. The point - knowing about existence is like knowledge in general - a matter of necessity, prompted by the matter of fact.

As to what the concept of existence is. First, speaking generally, it is the quality of presence in the totality, or the rejection of the absence from the totality of things. In other words, it is a statement about the world. Your being posits that you are part of this totality and have agency in the universe. This is both vacuous and necessary. If you were not a part of the totality, then your reasoning wouldn't make sense. Thus, to think that you are not part of the totality is a contradiction. The key is - are you an absurdity? You either exist sensibly and think that you are, or you exist non-sensibly and think that you aren't (which will devolve and obstruct your agency in the world), or you don't exist, and you have no thoughts, or you don't exist and our logic is unsound, the universe is absurd, and your thoughts have no truth value. Which my reasoning (and probably yours) opposes instinctively, because it uses logic to operate. Which isn't a matter of choice.

A few caveats. There is also the question - how do you know that the world reveals the actual totality, and not a subset of it. You don't. Although, you act like you do by necessity.

Finally, from the point of view of spirituality, the above does not exhaust the question. But I don't think that there is anything spiritual that can be conveyed on that subject without some kind of specific meta-language and conceptualization of a different kind. Spirituality isn't a logical subject matter to begin with.

To steal from Descartes, if I am questioning my existence then I must exist, because how else could I be questioning if I exist?

One cannot not know he exists unless he exists. One can only doubt his existence if he exists. Existence is a precondition to both knowing and doubting.

Bronson. In stealing from Descartes you are making the same mistake that he made in his "Meditations". The "existing I " whose existence needs to be proved, is used as a premise to prove its existence. In other words, its a logical fallacy - the "petitio principii". (But, granted, superficially viewed, it looks like a perfectly valid argument.)

The reason to doubt your existence is a consequence of the difficulty to proof your existence — Daniel C

Either prove that P or it's implied that one must doubt that P is quite the false dichotomy.

Terrapin Station. It seems, if I understand you correctly, that proving P is like proving A, M, Y and Z. If that is the case and P is equal to existence, it seems that a category mistake is being made, because P is the prerequisite for any other attributes like A,M,Y and Z to exist and therefore belongs to a different logical category. I fail to see why it is needed "that one must doubt that P is quite the false dichotomy". Some clarification on this point will be helpful.

I think w

Every person, as a self, body, or both, knows they exist. But that knowledge is certainly variable with concern to each one, as a lot of philosophies about proving one's existence have emerged, and are known for their common contradictions.

What's yours? I would like to hear from you. — Unlimiter

I think what's more disorienting and freaky is the thought that nothing really validates our own collective existence. I mean everything is materially continuous, and without our brains placing meaning and significance on the intrinsic patterns in the universe, and distinguishing tables from chairs, dogs from cats; there'd be nothing to do so.. it would just be what it always was; one blob of matter in motion.

All of those things we distinguish from surroundings, we do because of very human-centered reasons. An intelligent agent with a completely different set of sensors and body design may find other distinctions relevant to it and may completely discount our existence because to form a visual boundary around and define a 'human' or 'dog' or 'cat' may completely be irrelevant to it. Maybe its brain operates on a timescale of hundreds of years as opposed to miliseconds, or nanoseconds as opposed to miliseconds and so it just misses us; maybe it's so tiny it finds objects on the bacterial scale of size relevant. etc. But the point is, there's nothing really substantiating our existence; we just collectively validate each other's existence because we interact with each other.

This is wrong. Descartes doesn't presuppose, or beg the question of, the existence or reality of the “I” as a premise. Thinking that is a result of a superficial view of Descartes’ work, & not the contrary.

Descartes doesn’t merely presume, as you’d have it, the “I” as a premise, indeed, he demonstrates (so it cannot be a mere presumption) that, when in doubt, doubting its existence is impossible (while doubting virtually everything else is possible, like the reality of external things [after all, these could all possibly be mere items of a dream, i.e., perception-dependent objects]), such that the reality of it is immediately perceived in this very particular moment of attempting to do so. Thus no presumption, but immediate perception.

In one of his replies to the objections to the Meditations, he even addressed this himself, "When someone says, 'I am thinking, therefore I am, or I exist', he does not deduce existence from thought by means of a syllogism, but recognizes it as something self-evident by a simple intuition of the mind. This is clear from the fact that if he were deducing it by means of a syllogism, he would have to have had previous knowledge of the major premise, 'Everything which thinks is, or exists'; yet in fact he learns it from experiencing in his own case that it is impossible that he should think without existing."

On what ground can it be doubted?

aRealidealist. (1)"Thus no presumption, but immediate perception". Immediate perception here is strongly subjective and Descartes must have realised this; therefore his attempt to construct a more rational and objective proof for existence.
(2) ".....it is impossible that he should think without existing". Exactly. Therefore - because thinking without existing is impossible - thinking proofs that we exist! (With all its further implications …..)

Therefore - because thinking without existing is impossible - thinking proofs that we exist! — Daniel C

We assume that thinking is real, because we are thinking, and we exist. If we didn't exist, any consequence of us thinking, which includes being, and contradicts us not being, would also require us to be in fact. I agree with . I don't think we can conclude our own existence logically. We may not need to.

PS. Although in terms of the argument between aRealidealist and Daniel C, I have no idea whether Descartes proved or witnessed his existence. Daniel C is at least correct that the usual interpretation of Descartes by most people (including my illiterate self) is that reason is evidence for being in fact. I am also not arguing whether we exist. But I don't think that assuming existence is a choice.

We don't exist, except for ourselves?

Works for me.

Only other people die, in my experience.

Existential dread may also be how we know we exist. It being at the center of the human condition. — Anthony

A better approach would be the Sartrean stare. You know you exist when someone looks at you with contempt.

Cogito ergo sum. — Artemis

I prefer

I just ate some kielbasa. — Terrapin Station