The idea is undercut because it uses the means of verification that are being denied in order to promote the proposition.

You've demonstrated that it's possible to doubt it. That shows that the knowledge most be a posteriori. Yet, if you haven't seen it, what experience do you base the knowledge on?

Yet, if you haven't seen it, what experience do you base the knowledge on? — Tate

:up: :100:

The question reminds me of predator-prey eye positions. Prey have eyes on the sides of their head, giving them a 360^o field of vision in order to detect approaching predators. Predators, on the other hand, have front-facing eyes for stereoscopic/binocular vision so that they can judge distance accurately during a hunt. Predators can't see behind; prey can and still they get caught. Oh bummer!

I

You've demonstrated that it's possible to doubt it. — Tate

Is it possible coherently to doubt it? If it's true, all statements about the past are false. In that case, I didn't write the last sentence. I did not believe that I was writing it. I have not read the OP or looked at the quora link. There was no link.

How do we know there is a behind us? — Darkneos

The problem, mon ami, is we don't even know if there's a front us!

:cool:

Is it possible coherently to doubt it? — Cuthbert

I don't think it's possible to doubt that there is space behind me. I apparently know that there is space a priori.

But as for objects occupying that space, I can imagine that a void follows me around, so I can doubt the objects. That means if I have knowledge of them, it's a posteriori.

If it's true, all statements about the past are false. — Cuthbert

Could you explain why?

Could you explain why — Tate

Alas, no, because I misread the whole thing. I thought it was about whether we can doubt that any time exists except the present.

I suppose if there is no world out there (the doubt is coherent and the hypothesis happens to be true), but there is a past and there are other people, then it becomes testable. I could ask my friend, who was on the other side of the door, whether the world continued to exist while I had the door closed. Do that a few times in different circumstances and I might begin to wonder whether my being on my side of the door is wholly irrelevant to the question of what is on the other side of it. It sounds like a project for a baby of 4 - 6 months, when we are getting used to the idea that teddy hiding is still teddy.

I suppose if there is no world out there (the doubt is coherent and the hypothesis happens to be true), — Cuthbert

The question isn't about whether there's a world. It's about whether there's anything behind you.

@Tate Yes, I got that. After a slow start. My answer is to ask a friend to look and check for me. The world and other people exist - it's just 'behind' that's the problem - so the question can be settled.

Yes, I got that. After a slow start. My answer is to ask a friend to look and check for me. — Cuthbert

You can't do that continuously though.

As I mentioned, the knowledge that there is space behind you is probably a priori because you can't doubt it. If you tried to imagine no space, that would conflict with the idea of 'behind '

So you know there is space a priori. How do you know there are predictable objects behind you? I think that's part of a dynamic model that's coming from you. In other words, it's a hypothesis. You don't know what's behind you until you do ask a friend, or turn around.

How do you know? You just do. Let's also not forget that there are dire consequences for doubting a behind you. Try breaking hard in traffic and see the legitimacy of such a doubt.

Pretty sure we do.

The only sensible answer is to keep turning around, faster and faster, until you puke.

Pretty sure we do. — Darkneos

Deus deceptor? The whole thing could be a one giant illusion (maya). Magick! The question of front and behind or on the sides is moot.

How do you know? You just do — Darkneos

Sure. You know there's "stuff" behind you. That's a model.

I don't consider that possibility valid.

More like reality, no amount of philosophical musing will change that.

I don't consider that possibility valid — Darkneos

It is only an extension of your "behind us" idea which is basically a reserved skeptical argument; I just went the whole nine yards mon ami and let the seed you planted bloom in full glory.

More like reality, no amount of philosophical musing will change that. — Darkneos

Especially if you don't do any philosophical musing.

There is no seed, it's a non starter and not to mention not even related to the behind you question.

Whether you do or don't it won't change that there is something behind you. Though it does say something how philosophical musings don't change reality, sometimes it makes me question why even bother asking such questions.

There is no seed, it's a non starter and not to mention not even related to the behind you question — Darkneos

Ok!

sometimes it makes me question why even bother asking such questions. — Darkneos

Well, there you have it.

You don't know what's behind you until you do ask a friend, or turn around. — Tate

I wouldn't say that's always true. As I write, my kitchen is behind me. You did not know that - but I did. That's a difference of the states of knowledge betwen us. If we deny knowledge to both of us - to you, because you have no idea where my kitchen is, and to me, because it's behind me - then I'm not sure how to express the clear difference between us in respect of knowledge. It seems as if there was a clear difference and now a theory has been introduced to smudge it or invalidate it. My first instinct is to doubt the theory and to preserve the phenomena - the phenomena in this case being that I do know which room is behind me, even without turning round, and most other people don't know.

What theory is causing the problem? Perhaps it's something like this: "If it's possible to doubt something, then the knowledge of that thing must be a posteriori [dependent on experience]." We now have a counter-example. It's possible for me to doubt that my kitchen is behind me. I can't see it. And still I have knowledge that it's there right now, because there is a clear distinction between the knowledge that I have and the knowledge that most people lack. So I have knowledge of something which it's possible to doubt and yet my knowledge is not based on up-to-the-minute experience. I don't have a problem with that. It's an interesting observation.

Yet you have neither empirical nor logical proof. That's the interesting part.

You do have logical proof though and to a lesser extent empirical.

You do have logical proof though and to a lesser extent empirical. — Darkneos

What's the logical argument?

Imagine an infinitely large line of people or a line of people that goes all the way around earth. Every person in each scenario has a person in front and another person behind them; in addition, each person is in front and behind two other people. Imagine you are the leftmost in a group of three people from one of these lines. How would you explain that the person in front of you is the person in front of you when that person is in the "behind" of someone else? In fact, how would you explain your existence when you are someone else's behind?

If existence is tied to perception (existence $\to$ perception), what we don't perceive doesn't exist (modus tollens). However, what is behind us is what we can't perceive i.e. it is a limitation imposed by our body structure (eyes are looking in one direction only) and that's what we call a confounding factor that simply can't be removed from the equation much to our disadvantage. The point then is to distinguish two kinds of non-perception viz. don't & can't kinds. What I don't perceive (front of us ) doesn't exist, but what I can't perceive (behind us) may exist.

Furthermore, Perception $\to$ Existence [Hallucination (mental illness/drug-induced)]. In other words there are no sufficient conditions, if perception is our benchmark, to decide whether something exists or not. We are left with only the ability to disprove existence (existence $\to$ perception) via modus tollens, but not prove it.

As is obvious to the reader, contrary to what we've been thinking all along, we don't have a definition of existence if perception is our standard/measure. Odd that!

Nothing exists [...] — Gorgias

Skepticism ne plus ultra.

Imagine an infinitely large line of people or a line of people that goes all the way around earth. Every person in each scenario has a person in front and another person behind them; in addition, each person is in front and behind two other people. Imagine you are the leftmost in a group of three people from one of these lines. How would you explain that the person in front of you is the person in front of you when that person is in the "behind" of someone else? In fact, how would you explain your existence when you are someone else's behind? — Daniel

Yes, we can't delete "behind" from the English language. Our philosophy super powers aren't that strong. :groan:

We spend so much time wiping our behinds, I don't see how we can't know that we each have one. If, then, we each have a behind, it follow there's always one behind us.

Watch out, the world's behind you
There's always someone around you who will call
It's nothing at all — Velvet Underground, Sunday Morning

https://www.youtube.com/watch?v=N3Oc9C3EHLo