Right. Which is to say that it has no definite identity. Which is another way of calling into question its actual existence. Which in turn has a lot to do with the whole Einstein-Bohr debate. — Wayfarer

As far as scientists can tell, all physical systems are quantum and so will produce the same quantum behavior as microscopic particles (one example is a visible piezoelectric tuning fork comprising about 10 trillion atoms). So the issue of identity and existence applies equally to large systems as small.

In general, history is very important. Have you heard of Richard Gregory's top-down theory of perception? — Magnus Anderson

No, but I take history into account by including in the definition of an object the object's position in spacetime.

By 'identical' I mean similar in every detail; exactly alike. — believenothing

Language doesn't work in the way presumed here. The meaning of terms such as "identical' changes with its use - or rather, we should think of its use rather than its meaning.

So Venus is variously called Phosphorus in the morning sky, Hesperus in the evening sky. Are they not identical?

1+1 = 2. And one plus one equals two. Are these equations - one in words, the other in numbers - identical?

One could continue citing examples of such equivocating expressions. THe point is that it depends on what you are doing.

By not paying the attention due to the language being used, the replies here amount to nothing.

Like most of philosophy.

I agree. Particles effect human action and a pair of identical twins with out a doubt have particles in different locations despite the fact that their dna is identical or close to identical. Even if the difference is what would commonly be called a trace difference. (such as humans have a trace amount gold in their bodies). If one twin wore a gold ring and the other didn't, one would probably have slightly more gold in his/her system. Gold to some extent is good for the human body.

Identicality isn't a description of appearances, it is an adopted convention that grants the inter-substitution of two or more distinguishable things in every situation. As an adopted convention, it doesn't make sense to ask whether two things really are identical.

Fantastic, thanks a lot. I often struggle with conventions though. I should say I struggle with language more often. I feel relieved to find I was barking up the wrong tree.

I don't understand what two "identical ideas" look like so I can't begin to answer the question.

If you read the same thing in two different books, such as a quote, then let me suggest you have seen the same 'idea' twice or in other words two identical ideas - all be it from different sources. Also 1+1=2 is something that will appear many times, so it's also kind of a repeated idea or identical idea. I'm not sure how to explain my perspective.

By not paying the attention due to the language being used, the replies here amount to nothing.

Like most of philosophy.

It seems I don't really spend enough time contemplating things in order to be able to contribute much to this site. I'm trying to dable though. Whether responses on this site amount to nothing or not, I'm glad this site exists and people still have time to share things on here.

I think I will continue to enjoy reading from my replies as long as I have breath.

Do you mean that the particle has a position in a point of space like the escaped convict and the quantum wave is only an expression of our incomplete knowledge of the particle's position? This idea was refuted by experimental tests of Bell's theorem: no local hidden-variable theory can be a correct description of quantum mechanics, where the hidden variable is a single point position of a particle, for example. This doesn't rule out non-local hidden-variable theories such as Bohm's but these theories seem incompatible with special relativity because they introduce superluminal speeds. — litewave

Thank you for the clarification. What I actually meant was just as after the search is actually conducted and the convict's location is discovered s/he will be found in one location, the particle too will be localized to one location. It isn't the case that quantum theory is claiming the particle is in two or more locations at once: the quantum wave merely indicates that the particle's position is uncertain. IF the quantum wave is actually saying the particle is in more than one location at the same time then why do we need probability in the first place? Simply say that the particle is in whatever location and also in another location.

Identity can also be (and it mostly is) established by history. So two objects can occupy the same position in space at the same time and still be identified as two different objects simply because they have different histories. — Magnus Anderson

I agree but only partially because history isn't exact enough as the requirement that it's impossible for one object to be in more than one location at the same time. Imagine two paintings A and B that are in the same gallery and is the work of the same artist. The histories of both A and B are identical and that, if history defines identity, would mean A and B have the same identity which strikes me as preposterous. Every relevant parameter could be manipulated to make A and B have the exact same history and yet it wouldn't feel right to say A and B had the same identity.

IF the quantum wave is actually saying the particle is in more than one location at the same time then why do we need probability in the first place? Simply say that the particle is in whatever location and also in another location. — TheMadFool

I see the quantum wave as an object whose mathematical (quantitative-structural) properties specify how it will interact with other objects. I don't mean that a quantum wave is less "real" than a point particle; it's just something that is there, although a different something than a point particle. The probabilistic character of the quantum wave is of course at the heart of interpretations of quantum mechanics. Currently I prefer the many-worlds interpretation because it doesn't seem to need more assumptions beyond the Schrodinger equation of the quantum wave, like wave "collapse". It just assumes that the quantum wave evolves according to the Schrodinger equation, with the mathematical consequence being that when the wave interacts with a many-particle object, parts of the wave that correspond to different possible values of a variable (for example, point position) stop interfering with each other and become separated into non-interacting parts of reality ("worlds").

A problem with the many-worlds interpretation is that an infinite number of possible values of a variable corresponds to an infinite number of worlds and it is not clear how to calculate frequentist probabilities when there is an infinite number of possibilities. Maybe a reconciliation of quantum mechanics with relativity theory will provide a solution to this problem, perhaps by limiting the number of possibilities to a finite number.

If you agree then imagine four objects A, B, C, and D and that there are only 4 possible properties: round, square, red and black.
A is a red and round
B is red and square
C is red and round
D is black and square.

Using "=" to mean "identical to" we conclude that A = C but A not = B and B not = C and so on. Identicalness, in this sense, means all properties must match exactly. — TheMadFool

This is an incorrect example because of the deficiencies of the human capacity of identification. The law of identity places a thing's identity within the thing itself, (a thing is the same as itself), not in what we say about the thing. So A is not necessarily the same as C because your premise "there are only 4 possible properties" is a faulty premise.

I think that metaphysical identity deals with physical identity. But even aking your example, reading the same thing at 3 am would evoke a different image/interpretation than reading it at 3 pm.

If you’re not very familiar then you may not be aware of this:

https://en.wikipedia.org/wiki/Law_of_identity

If you are then exactly what are you talking about that isn’t covered by this law? Identity is necessary for identifying - the idea of ‘identical’ is pretty much the basis of propositional logic and the means for common communication rather than having a constantly shifting perception of reality that remains wholly distanced from the next moment, person or thought.

Much like the question of ‘what happens when an unstoppable force meets an unmovable object?’ The answer is so startlingly obvious we don’t appreciate it straight away. The answer is we either don’t ‘see’ what happens, or we reestablish our concepts for ‘unstoppable’ and ‘unmovable’ - perhaps identifying a new concept to explain the phenomenon (a modern example would be the phenomenon of quantum - we name it and then investigate further to identify what is happening).

The issue is an epistemic one.

This is an incorrect example because of the deficiencies of the human capacity of identification. The law of identity places a thing's identity within the thing itself, (a thing is the same as itself), not in what we say about the thing. So A is not necessarily the same as C because your premise "there are only 4 possible properties" is a faulty premise. — Metaphysician Undercover

I only used 4 properties to simplify the issue and the number 4, in and of itself, has no bearing on the critical aspects of identicalness which is, quite obviously, based on shared properties. The only method by which we may distinguish objects is on the basis of differences in properties and the only method by which we may say two or more objects are identical is by checking if they share all properties or not.

I see the quantum wave as an object whose mathematical (quantitative-structural) properties specify how it will interact with other objects. I don't mean that a quantum wave is less "real" than a point particle; it's just something that is there, although a different something than a point particle. The probabilistic character of the quantum wave is of course at the heart of interpretations of quantum mechanics. Currently I prefer the many-worlds interpretation because it doesn't seem to need more assumptions beyond the Schrodinger equation of the quantum wave, like wave "collapse". It just assumes that the quantum wave evolves according to the Schrodinger equation, with the mathematical consequence being that when the wave interacts with a many-particle object, parts of the wave that correspond to different possible values of a variable (for example, point position) stop interfering with each other and become separated into non-interacting parts of reality ("worlds").

A problem with the many-worlds interpretation is that an infinite number of possible values of a variable corresponds to an infinite number of worlds and it is not clear how to calculate frequentist probabilities when there is an infinite number of possibilities. Maybe a reconciliation of quantum mechanics with relativity theory will provide a solution to this problem, perhaps by limiting the number of possibilities to a finite number. — litewave

As you can see, any interpretation, wave collapse or many worlds, is clearly born of the difficulty in accepting that one object can occupy different locations at the same time or some variation of that theme. Wave functions collapse and the particle is detected in one of the many locations instead of being at all of them at once. Many worlds exist precisely because each possibility would require a different location to be actualized.

I only used 4 properties to simplify the issue and the number 4, in and of itself, has no bearing on the critical aspects of identicalness which is, quite obviously, based on shared properties. The only method by which we may distinguish objects is on the basis of differences in properties and the only method by which we may say two or more objects are identical is by checking if they share all properties or not. — TheMadFool

The point was to show that your approach is faulty. Identity is based in uniqueness, and this is the opposite of "shared properties". So you'll never get to the true meaning of "identical" through the assumption that "identicalness" is based in shared properties, because it's not, it's based in "identity", and identity refers to uniqueness..

"Can anything ever be identical?

Beyond the necessary truism that everything is self-identical, methinks the answer is no.

The point was to show that your approach is faulty. Identity is based in uniqueness, and this is the opposite of "shared properties". So you'll never get to the true meaning of "identical" through the assumption that "identicalness" is based in shared properties, because it's not, it's based in "identity", and identity refers to uniqueness.. — Metaphysician Undercover

Firstly we seem to be on the same page. Secondly you didn't read my post but that's ok because there's nothing that isn't obvious in it.

what are you talking about that isn’t covered by this law? Identity is necessary for identifying - the idea of ‘identical’ is pretty much the basis of propositional logic

thanks, i think. I was just telling a friend i might have some reading to do. That was before I logged into this site, spooky eh? I'm not so sure what I do with my time. So called book knowledge was never my forte. Too many alternatives- i mean alternative books and/or sources. I still think too much knowledge can be a bad thing.

A=A. — Wayfarer

Does it mean I am myself? My first name starts with an "A".

Then what happens when I'm beside myself? Am I still identical to myself?

Or let's suppose I cloned myself. On the other hand, let's not suppose that.

I still think too much knowledge can be a bad thing. — believenothing

Knowledge is power. And don't you forget that.

Power is something else.

Something else is something else again.

And don't you forget that.

This is the most powerfully useful idea in all of philosophy.