If you include things like time and position then two objects can never be identical

Thanks khaled, but what about ideas or concepts? I mean not just 'real' objects? Could your observation be identical to what you believe after reading it? If someone can come up with something that can be identical then I would have something else to think about for a while. Do you know what I mean?

Can a difference always be established? Or is there a point at which all possible perspectives agree that there is no difference at all?

I'm trying to ask about uniquity and originality and that sort of thing, but also trying to learn more about limits.

だけに

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.

I don't understand what two "identical ideas" look like so I can't begin to answer the question. Also there is a little arrow under every message that lets you reply so the person you're replying to gets notified. I only noticed this reply by chance

In that sense it would be pretty hard to argue that when I talk about an apple and an orange, a dog and a cat, or a toilet, a shovel and a toadstool, that each iteration of ‘and’ is anything but ‘identical’.

There are several terms like this that transcend languages - the most obvious being numbers. In every language the number ‘one’ is the same number one not a different number ‘one’. That said, there is differences in each person’s lexicon and experience, so I may associate certain ‘universal terms’ like these with experiences that aren’t ‘universal’ - the meaning, in the purest sense of the term, does remain identical though.

As a rule of thumb any ‘abstract’ term - not concrete nouns - is identical, yet it’s use is rarely, or maybe never, used in an identical way (as above with the example of items listed). Remove items located in time and space and you’ll find many identical items of thought such as conjunctions and identifiers.

An old Hungarian puzzle for kids:

"What's the difference between a sparrow?
?
Both of its wings are identical, especially the left one."

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Someone said that if we count position and placement, then eSPECIALLY can't two objects be the same.

It is conceivable, however, that the wardrobe chest I just got delivered to my house made of compressed wood contains two identical wardrobe chests, both occupying the same space at the same time and in the same respect.

With what?

As an adopted convention, it doesn't make sense to ask whether two things really are identical. — sime

Like the morning and evening star, water and H2O, temperature and molecular motion, Samuel Clemens and Mark Twain, the empty set and 0, or the charge of every electron in the universe.

Or that damned ship that had all its parts replaced during its voyage.

If you include things like time and position then two objects can never be identical — khaled

There is a the one-electron universe hypothesis where all the electrons and positrons are just one entity traveling back and forth through time, thus explaining how they all have identical mass and charge.

Setting that idea aside, even if physical objects can't be identical, some properties do have that quality. Leading us to ...

Universals (or Tropes).

た世界を選

A=A.

Always, invariably, in all circumstances.

Like the morning and evening star, water and H2O, temperature and molecular motion, Samuel Clemens and Mark Twain, the empty set and 0, or the charge of every electron in the universe.

Or that damned ship that had all its parts replaced during its voyage. — Marchesk

Well obviously in each case, the terms on the left and right side do not possess the same sense, so are not practically substitutable, so are only substitutable in a theoretical sense that makes potentially falsifiable counterfactual claims. Now standard dogma alleges that Superman is only de dicto different from Clarke Kent, but that de re they are one and the same person.

" In the context of thought, the distinction helps us explain how people can hold seemingly self-contradictory beliefs.[4] Say Lois Lane believes Clark Kent is weaker than Superman. Since Clark Kent is Superman, taken de re, Lois's belief is untenable; the names 'Clark Kent' and 'Superman' pick out an individual in the world, and a person (or super-person) cannot be stronger than himself. Understood de dicto, however, this may be a perfectly reasonable belief, since Lois is not aware that Clark and Superman are one and the same. " - https://en.wikipedia.org/wiki/De_dicto_and_de_re

Yet in "Superman 3" Superman was poisoned and divided himself into Evil Superman and Clarke Kent who then fought a physical fight. I submit this as evidence that Superman is not Clarke Kent de re .

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

See identical particles which are indistinguishable in principle.

As for sub-atomic particles - do they have any identity, if they don’t even have a position? I mean, electrons and photons notoriously manifest as waves in some contexts, and particles in others. So if they don’t have an identity prior to measurement then they're indistinguishable as a matter of principle - as you say - but perhaps not in the way you mean.

I think everything is unique in some way or other. If two things appear to be identical they would still be different if they are in different locations for example. — believenothing

This is Leibniz' principle, "the identity of indiscernibles". It states that if two objects can be said to have the very same properties, then they are identical. "Identical" means having the same identity, and by Aristotle's law of identity, this means that they are actually one and the same object. Therefore it is incorrect to say that this is "two objects", because it is actually one and the same object being referred to. The law of identity, "a thing is the same as itself" represents the uniqueness of every object. Essentially, it says that an object is unique.

It is conceivable, however, that the wardrobe chest I just got delivered to my house made of compressed wood contains two identical wardrobe chests, both occupying the same space at the same time and in the same respect. — god must be atheist

You can say this, that two distinct things can occupy the exact same place, at the exact same time, but is this really conceivable? There is a difference between what you can say, and what you can conceive. To actually conceive of what you say here, you would need a conception of the spatial temporal existence of an object which would allow for this. I believe that "multiverse" theorists allow that the same object exists in many distinct universes, and multiverse theory is supported by the many-worlds interpretation of quantum mechanics. This allows one to say that the same object is many objects, separated by being in many universes. However, if the multiple wardrobes you refer to, are actually in separate universes, it would not really be correct to say that they occupy the same space at the same time, because the particular space and time being referred to is a property of the particular universe..

As for sub-atomic particles - do they have any identity, if they don’t even have a position? I mean, electrons and photons notoriously manifest as waves in some contexts, and particles in others. So if they don’t have an identity prior to measurement then they're indistinguishable as a matter of principle - as you say - but perhaps not in the way you mean. — Wayfarer

Part of a quantum particle's identity is that it can have amplitude for two or more positions (i.e., a superposition).

This is just a different notion of identity to the classical idea where particles always have a definite position and momentum.

This is just a different notion of identity to the classical idea where particles always have a definite position and momentum. — Andrew M

What if it's not 'a different notion of identity', but that it's not an identity at all. There are not two things which are identical. It is said that particles aren't even particles until they're measured, prior to that literally all that exists is a distribution of possibilities. It's not as if there's a particle whose whereabouts is unknown, it doesn't have an exact whereabouts, so also does not have an identity. In fact couldn't you say that the measurement is what confers identity on it, by giving it a position and making it 'this particle'?

If two things appear to be identical they would still be different if they are in different locations for example — believenothing

Correct. The presence of a difference precludes identicalness. Two objects are identical if and only if they both possess the exact same properties. This definition uses properties as defining elements of objects; objects here meaning anything and everything.

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.

Bear in mind the identicalness is not the same as identity. The former is a relationship between objects as we've seen above but the latter is not. Identity is, as you so rightly noted, uniqueness which in mathematical terms is one and so, because relationships require at least two objects, identity isn't a relationship.

To further clarify the difference between identicalness and identity we need to understand that identicalness doesn't consider space-time properties as relevant to its meaning. That's why when we're presented with two cars of the same model we usually say that they're identical. That the two cars occupy different spatial location is not relevant to identicalness. Similarly that one car was produced five minutes after the second car doesn't matter so long as they're the same model. In short space-time properties are irrelevant to the concept of identicalness.

When it comes to identity, matters are different and space-time properties are critical to its meaning. One object cannot occupy two locations in space at the same time and it is this impossibility that gives objects their identity. So, two/more objects can be identical because they share all properties except space-time properties but they all have different identities because one object can't occupy two locations in space at the same time.

I dont think an item or concept could be identical with itself either, because things change over time and the only way I can imagine to prove — believenothing

If we look at how I defined identicalness then it's true that any object possesses all the properties it has and so it follows that an object is identical to itself.

Remember I said earlier that relationships require at least two objects. This isn't entirely true as is evidenced by the claim above that a = a or A = A but this can be understood in terms of identicalness in identity being only reflexive - oneness preserved.

This is codified in logic as the law of identity as a = a for objects and A = A for propositions.

This is necessary for the reason that in any discourse the meaning or words and sentences shouldn't change otherwise humorous but dangerous events will occur. For example this could happen:

1. Only man is intelligent
2. No woman is a man
So
3. No woman is intelligent

In the above argument the meaning of "man" has changed from "humans" in 1 to "male" in 2 which leads us to wrong albeit funny conclusion. The law of identity exists to prevent such things from happening.

who remembers will always be different from what remembers — armonie

:up:

An old Hungarian puzzle for kids:

"What's the difference between a sparrow?
?
Both of its wings are identical, especially the left one." — god must be atheist

:lol:

This is Leibniz' principle, "the identity of indiscernibles". It states that if two objects can be said to have the very same properties, then they are identical. "Identical" means having the same identity, and by Aristotle's law of identity, this means that they are actually one and the same object. — Metaphysician Undercover

Read my reply to the OP

What if it's not 'a different notion of identity', but that it's not an identity at all. There are not two things which are identical. It is said that particles aren't even particles until they're measured, prior to that literally all that exists is a distribution of possibilities. It's not as if there's a particle whose whereabouts is unknown, it doesn't have an exact whereabouts, so also does not have an identity. In fact couldn't you say that the measurement is what confers identity on it, by giving it a position and making it 'this particle'? — Wayfarer

It's not so straightforward. While a position measurement makes the position definite (within the measured range), it also makes the momentum indefinite (i.e., the particle is now in a superposition of momenta). So the state of a particle always has at least some indefinite properties (due to Heisenberg uncertainty), regardless of whether the particle is measured or not.

One object cannot occupy two locations in space at the same time and it is this impossibility that gives objects their identity. — TheMadFool

Yes, I would just add that this depends on how the object is defined. For example, in a sense it is true that my desk can occupy two locations in space at the same time - one leg here, another leg there! That's because the desk is defined as an object that is extended in space. But if by "location" we mean the spatial extension of the desk then it is true that the desk cannot occupy two locations in space at the same time - because it would violate the definition of the desk and so we would be talking about a different object than a desk.

This should be kept in mind when interpreting quantum mechanics. There is no point particle that occupies two points of space at the same time, but there is a quantum wave, defined as a spatially extended object, that occupies two or more points of space at the same time. Alternatively (and equivalently, if I understand it correctly), there is a point particle that occupies two points of space at the same time if the definition of the "point particle" allows the particle to move not only forward but also backward in time.

Yes, I would just add that this depends on how the object is defined. For example, in a sense it is true that my desk can occupy two locations in space at the same time - one leg here, another leg there! That's because the desk is defined as an object that is extended in space. But if by "location" we mean the spatial extension of the desk then it is true that the desk cannot occupy two locations in space at the same time - because it would violate the definition of the desk and so we would be talking about a different object than a desk.

This should be kept in mind when interpreting quantum mechanics. There is no point particle that occupies two points of space at the same time, but there is a quantum wave, defined as a spatially extended object, that occupies two or more points of space at the same time. Alternatively (and equivalently, if I understand it correctly), there is a point particle that occupies two points of space at the same time if the definition of the "point particle" allows the particle to move not only forward but also backward in time. — litewave

As far as I understand the quantum wave is just the probability of where a particle is located. That there are two different locations in the probability doesn't imply the particle is in different locations at the same time.

Imagine an escaped convict being hunted by the law. The search party would need a plan to find the escapee and it could take the following form: he needs water so he maybe along the river; he needs to avoid detection so he may be in the forest; he needs food so he maybe around a town; etc. There's a probability that he maybe in all of these locations but that in no way implies he's in all of them at once at the same time.

So the state of a particle always has at least some indefinite properties (due to Heisenberg uncertainty), regardless of whether the particle is measured or not. — Andrew M

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.

As far as I understand the quantum wave is just the probability of where a particle is located. — TheMadFool

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.

In general, two things are identical if and only if everything that makes up the first thing also makes up the second thing and vice versa.

The more important question, perhaps, is what constitutes a thing. Who decides what constitutes a thing? Us, of course.

Let's say we have two apples both of which are completely identical except in one regard: they occupy different positions. Are they identical or not? The answer depends on whether an apple's position constitutes its identity. In general, the answer is no, since we all operate with the concept of apple according to which an apple remains the same apple regardless of its position in space. Therefore, we can conclude, the two apples, though occupying two different positions, are identical.

If two things appear to be identical they would still be different if they are in different locations for example. — believenothing

In most cases, that amounts to sophistry, since position is rarely part of an object's identity.

When it comes to identity, matters are different and space-time properties are critical to its meaning. One object cannot occupy two locations in space at the same time and it is this impossibility that gives objects their identity. So, two/more objects can be identical because they share all properties except space-time properties but they all have different identities because one object can't occupy two locations in space at the same time. — TheMadFool

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.

Let's say we have two apples both of which are completely identical except in one regard: they occupy different positions. Are they identical or not? The answer depends on whether an apple's position constitutes its identity. — Magnus Anderson

We can also define the identity of an object by its relations to all other objects. The object's parts are only some of the other objects. Since the two apples have different positions relative to other objects, they have different identities. If they had the same positions relative to all other objects, they would have the same identity, which means they would be one apple, not two.

If they had the same positions relative to all other objects, they would have the same identity, which means they would be one apple, not two. — litewave

My point is, not necessarily.

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