Can we know that something doesn't exist?

Get Email Updates Email this Topic Print this Page

kennethamy
 
Reply Mon 8 Mar, 2010 04:02 pm
@Night Ripper,
Night Ripper;137655 wrote:
So you're using "physically impossible" to mean "inconsistent with relativity theory" instead of using "physically impossible" to mean "can't happen"?


If relativity theory is true, then it is physically impossible for anything to go faster than light. And what is physically impossible cannot happen. (Of course, what is physically impossible is any event inconsistent with a true scientific theory. Such an event cannot happen). The only event that cannot happen (period) is a self-contradictory event, so far as I can tell.
 
Zetherin
 
Reply Mon 8 Mar, 2010 04:22 pm
@kennethamy,
kennethamy;137673 wrote:
If relativity theory is true, then it is physically impossible for anything to go faster than light. And what is physically impossible cannot happen. (Of course, what is physically impossible is any event inconsistent with a true scientific theory. Such an event cannot happen). The only event that cannot happen (period) is a self-contradictory event, so far as I can tell.


I told you guys earlier that there are two sorts of "can't" being talked about here. There is the logically impossible can't which is a self-contradictory event, and then there is the physically impossible can't which means an event inconsistent with a true law of physics/scientific theory. We aren't saying 'period' with the latter.

And Night believes the two mean the same, I think.
 
kennethamy
 
Reply Mon 8 Mar, 2010 04:29 pm
@Zetherin,
Zetherin;137682 wrote:
I told you guys earlier that there are two sorts of "can't" being talked about here. There is the logically impossible can't which is a self-contradictory event, and then there is the physically impossible can't which means an even inconsistent with a true law of physics/scientific theory. You aren't saying 'period' with the latter.

And Night believes the two mean the same, I think.



Yes. I said "physically impossible" not "impossible". That is the difference between "logically impossible" and "physically impossible". (There are other kinds of impossibilities too(. E.G. technically impossible, and epistemically impossible.

In philosophy, clarification dissolves most problems. There was no disagreement, there was confusion.
 
Zetherin
 
Reply Mon 8 Mar, 2010 04:31 pm
@kennethamy,
kennethamy;137685 wrote:
Yes. I said "physically impossible" not "impossible". That is the difference between "logically impossible" and "physically impossible". (There are other kinds of impossibilities too(. E.G. technically impossible, and epistemically impossible.

In philosophy, clarification dissolves most problems. There was no disagreement, there was confusion.


Well, I have attempted to clarify. I have said exactly this I thought, but it has not helped. Perhaps it was my wording.
 
Night Ripper
 
Reply Mon 8 Mar, 2010 04:56 pm
@Zetherin,
Subjunctive possibility - Wikipedia, the free encyclopedia

Quote:
Types of subjunctive possibility

There are several different types of subjunctive modality, which can be classified as broader or more narrow than one another depending on how restrictive the rules for what counts as "possible" are. Some of the most commonly discussed are:

  • Logical possibility is usually considered the broadest sort of possibility; a proposition is said to be logically possible if there is no logical contradiction involved in its being true. "Dick Cheney is a bachelor" is logically possible, though in fact false; most philosophers have thought that statements like "If I flap my arms very hard, I will fly" are logically possible, although they are nomologically impossible. "Dick Cheney is a married bachelor," on the other hand, is logically impossible; anyone who is a bachelor is therefore not married, so the sentence involves a logical contradiction.


  • Metaphysical possibility is either equivalent to logical possibility or narrower than it (what a philosopher thinks the relationship between the two is depends, in part, on the philosopher's view of logic). Some philosophers have held that discovered identities such as Kripke's "Water is H2O" are metaphysically necessary but not logically necessary (they would claim that there is no formal contradiction involved in "Water is not H2O" even though it turns out to be metaphysically impossible).


  • Nomological possibility is possibility under the actual laws of nature. Most philosophers since David Hume have held that the laws of nature are metaphysically contingent--that there could have been different natural laws than the ones that actually obtain. If so, then it would not be logically or metaphysically impossible, for example, for you to travel to Alpha Centauri in one day; it would just have to be the case that you could travel faster than the speed of light. But of course there is an important sense in which this is not possible; given that the laws of nature are what they are, there is no way that you could do it. (Some philosophers, such as Sydney Shoemaker[citation needed], have argued that natural laws are in fact necessary, not contingent; if so, then nomological possibility is equivalent to metaphysical possibility.)


  • Temporal possibility is possibility given the actual history of the world. David Lewis could have chosen to take his degree in Accounting rather than Philosophy; but there is an important sense in which he cannot now. The "could have" expresses the fact that there is no logical, metaphysical, or even nomological impossibility involved in Lewis's having a degree in Economics instead of Philosophy; the "cannot now" expresses the fact that that possibility is no longer open to becoming actual, given that the past is as it actually is.

I'm talking about nomological possibility.
 
topnotcht121
 
Reply Mon 8 Mar, 2010 05:04 pm
@kennethamy,
I think that only through rationally we can know an object doesn't exist. But sometime rationality can lead to insanity. So if were not to exist, it wouldn't be capable of being used or experienced. Why would any human being deny existance? So, we can't "verify something that is not actual"
 
kennethamy
 
Reply Mon 8 Mar, 2010 06:29 pm
@Night Ripper,
Night Ripper;137691 wrote:
Subjunctive possibility - Wikipedia, the free encyclopedia

I'm talking about nomological possibility.


Yes, or physical possibility. Same thing.
 
Night Ripper
 
Reply Mon 8 Mar, 2010 07:10 pm
@kennethamy,
kennethamy;137712 wrote:
Yes, or physical possibility. Same thing.


Unfortunately it doesn't mention what you said.
 
kennethamy
 
Reply Mon 8 Mar, 2010 07:12 pm
@Night Ripper,
Night Ripper;137720 wrote:
Unfortunately it doesn't mention what you said.


What doesn't? ......... "Nomological possibility" (if that is what you are talking about) means, what is possible acccording to the laws of nature. If we consider the laws of nature together as physics, then that just comes down to physical possibility. Physical possibility is just what is consistent with physical law. Are you still having a problem?
 
Night Ripper
 
Reply Mon 8 Mar, 2010 07:30 pm
@kennethamy,
kennethamy;137721 wrote:
Are you still having a problem?


Yes, read what I quoted and explain to me why it says something different. Please actually address the text I've quoted.
 
kennethamy
 
Reply Mon 8 Mar, 2010 07:34 pm
@Night Ripper,
Night Ripper;137726 wrote:
Yes, read what I quoted and explain to me why it says something different. Please actually address the text I've quoted.


Which post? ............ I wish you would just say how what I said differs from the post on nomological possibility without all this dancing around. What does the post say that is inconsistent with what I said. It seems to me that they are both consistent.
 
ughaibu
 
Reply Mon 8 Mar, 2010 07:35 pm
@kennethamy,
kennethamy;137721 wrote:
Physical possibility is just what is consistent with physical law.
Does this indicate that you've officially relinquished the claim that physical possibility is defined by the deductive nomological theory?
 
kennethamy
 
Reply Mon 8 Mar, 2010 07:41 pm
@ughaibu,
ughaibu;137730 wrote:
Does this indicate that you've officially relinquished the claim that physical possibility is defined by the deductive nomological theory?


Not at all. I think that those two things are consistent. The DN model explicates that is means for an event to be consistent with the laws of nature. It must be deducible from them together with initial conditions.
 
Night Ripper
 
Reply Mon 8 Mar, 2010 07:55 pm
@kennethamy,
kennethamy;137733 wrote:
Not at all. I think that those two things are consistent. The DN model explicates that is means for an event to be consistent with the laws of nature. It must be deducible from them together with initial conditions.


You still haven't explained how that has anything to do with nomological possibility as talked about in Subjunctive possibility - Wikipedia, the free encyclopedia

I'm afraid you're just wasting everyone's time with these half-thought out answers. Your task is to convince us that something is physically impossible and that's going to require a complete argument, not bits and pieces sprinkled throughout different posts.
 
kennethamy
 
Reply Mon 8 Mar, 2010 08:05 pm
@Night Ripper,
Night Ripper;137736 wrote:
You still haven't explained how that has anything to do with nomological possibility as talked about in Subjunctive possibility - Wikipedia, the free encyclopedia

I'm afraid you're just wasting everyone's time with these half-thought out answers. Your task is to convince us that something is physically impossible and that's going to require a complete argument, not bits and pieces sprinkled throughout different posts.





e is physically possible if and only if, e is consistent with physical theory.
e is physically impossible if and only if e is inconsistent with physical theory.


Objections? Complaints? I don't mean general ones like, "you need a complete argument" You have to explain why it is that what I have just said is wrong or incomplete. No vague objections. . Just specific objections that I can address. Otherwise, save yourself some time.

And, to return (at long last to the OP) we can know that something does not exist if its existence would be physically impossible. For example, a man who jumped 100 feet into the air.
 
Night Ripper
 
Reply Mon 8 Mar, 2010 08:20 pm
@kennethamy,
kennethamy;137740 wrote:
e is physically possible if and only if, e is consistent with physical theory.
e is physically impossible if and only if e is inconsistent with physical theory.


You're giving a completely different definition of physically impossible than what was in that article earlier. I was just confused because you acted like you were talking about the same thing when, in fact, you're not.
 
kennethamy
 
Reply Mon 8 Mar, 2010 08:32 pm
@Night Ripper,
Night Ripper;137742 wrote:
You're giving a completely different definition of physically impossible than what was in that article earlier. I was just confused because you acted like you were talking about the same thing when, in fact, you're not.


The vocabulary is different. I don't see how the idea is any different. Maybe you do. If so, let me know. I think it is much the same. So it is up to you to tell my how I am wrong. Or, alternatively, you can just comment on my view.
 
Night Ripper
 
Reply Mon 8 Mar, 2010 08:46 pm
@kennethamy,
kennethamy;137745 wrote:
Or, alternatively, you can just comment on my view.


The truth of the theory of relativity implies that nothing ever accelerates faster than the speed of light. Therefore it's impossible for both the theory of relativity to be true and for something to accelerate faster than the speed of light. Since the theory of relativity is true, nothing does* accelerate faster than the speed of light.

(*It would be committing the modal fallacy to change that does to can.)
 
kennethamy
 
Reply Mon 8 Mar, 2010 09:00 pm
@Night Ripper,
Night Ripper;137753 wrote:
The truth of the theory of relativity implies that nothing ever accelerates faster than the speed of light. Therefore it's impossible for both the theory of relativity to be true and for something to accelerate faster than the speed of light. Since the theory of relativity is true, nothing does* accelerate faster than the speed of light.

(*It would be committing the modal fallacy to change that does to can.)


Not only nothing does, but nothing can (consistent with relativity). For if it could, then its doing so would be consistent with relativity, even if it did not. It is not only that nothing does go faster than light: is is impossible for anything to go faster than light, for if it did, relativity would be false.

Don't you think that some things that don't happen, can happen? And that some things that don't happen, can't happen. You don't think that the class of things that don't happen, and the class of things that can't happen, are the same class, do you?
 
Owen phil
 
Reply Mon 8 Mar, 2010 09:11 pm
@kennethamy,
kennethamy;137685 wrote:
Yes. I said "physically impossible" not "impossible". That is the difference between "logically impossible" and "physically impossible". (There are other kinds of impossibilities too(. E.G. technically impossible, and epistemically impossible.


What about Wittgenstein's Tractatus...

6.37 There is no compulsion making one thing happen because another has happened. The only necessity that exists is logical necessity.

6.375 Just as the only necessity that exists is logical necessity, so too the only impossibility that exists is logical impossibility.
 
 

 
Copyright © 2024 MadLab, LLC :: Terms of Service :: Privacy Policy :: Page generated in 0.03 seconds on 07/12/2024 at 08:37:48