Suppose a world Y is not actual. Why? There has to be a reason why that is.
— TheMadFool
There is a possible world in which my cat is ginger.

In the actual world, he is black.

Now the reason, if you need one, that the possible world in which my cat is ginger is not the actual world is that my cat is black. — Banno

Let me get this straight.

1. Your cat (in the actual world) is black

Therefore,

2. The possible world in which your cat is ginger is not the actual world.

The word "the" is key. Of course any possible world which differs from this (the) actual world is not this world. However that doesn't prove that those possible worlds are not actual. You're assuming that this (the) world is the only actual world.

Nuh. "Actual" is an indexical. Like left and right. The folk in each possible world think they are in the actual world.

Add that "Necessarily" is just "In all possible worlds", and hopefully you will see why your proposition is ill-formed. — Banno

The word "actual" as an indexical is not, I think, important. My argument has little to do with modal realism although we come to the same conclusion.

Your cat could not be ginger in any possible world, because it would not be the same cat. — Janus

Nuh. Jack - a rigid designator - might have been ginger. That sentence makes sense. It's exactly the sort of thing modal logic is intended to deal with.

Jack's identity is maintained across possible worlds.

You're assuming that this (the) world is the only actual world. — TheMadFool

Actually I explicitly said that the folk in each possible world think their world is the actual world.

But yes, there is only one actual world, within the structure of modal logic.

The word "actual" as an indexical is not, I think, important. — TheMadFool

If you think that, you've missed the point.

What's odd is that possible worlds should cause such confusion. The capacity for folk to miscomprehend is astonishing.

A new universe did not pop into existence when I pointed out that Jack might have been ginger*. It's just a way of talking about such possibilities that clarifies the relations of possibility and necessity. Mad, you are over-egging the ontology.


(*that sort of rubbish is the domain of quantum.)

Your reasoning still lies in the fallacy that I discovered.

This is what you say:

1. If X is an actual world then X is a possible world.

2. If X is a possible world then X is an actual world.

Consider now the following statement (contrapositive of 2)

3. If X is not an actual world then X is not a possible world (contrapositive of 2)

3. If X is not an actual world then X is not a possible world.

Undoing what we did, we get

4. If X is a possible world then X is an actual world (contrapositive of 3). This statement is true.

If X is an actual world (if apple is a fruit) then it is a possible world (a possible fruit) See how this argument is beginning to fall apart? You're stating that something real is a possibility of being real. This is a logical contradiction. Moving on.

If X is a possible world (a possible fruit) then X is an actual world (an actual fruit)

Still this doesn't make sense because as I said, the set of all possible conditions must be greater than the set of all actual objects. This is because a set of possible X should mean there is number of X that is not actual. The set of possible worlds therefore is greater than the set of actual worlds.

Therefore, we cannot say your second point as it is a logical contradiction. If X is a possible world it does not mean that X is an actual world because the set of X as possible worlds is bigger than the latter. Moving on.

You say in point 3 that if X is not an actual world then X is not a possible world. This contradictions everything you've said and been building up to so far. I can imagine a world that is made of gas, and although this planet is not real, it can be a possible world because it contains all the conditions of being real. For example, if something has possible properties then it is possible but not always actual.

Going to point 4 now which is built upon several logical mishaps, we will see that the conclusion must be false or at least doubtable. This can be done simply however.

Fourth point: If X is a possible world then X is an actual world. You just said in point 3 that if X is not an actual world then X is not a possible world. This is a complete contradiction to each other.

According to what you said, the set containing all possible worlds is equivalent to the set of all actual worlds. First of all "possible" means that there is a possibility that the world in question is not actual. This means that the set of possible worlds can never equal the set of actual worlds, because actual worlds are manifestations of conditions whereas possibility itself is a condition to be questioned. Therefore possibility is always superior in its set than actual manifestations of it, otherwise there is no need to use the word "possibility"- merely just call it actual- but before actuality there is always possibility and therefore the two cannot be equated to each other as you have done.

Actually I explicitly said that the folk in each possible world think their world is the actual world.

But yes, there is only one actual world, within the structure of modal logic. — Banno

I don't buy that. How can modal logic (about possibilities and necessities) ever even claim there is only one actual world.

If you think that, you've missed the point. — Banno

I believe you're barking up the wrong tree here.

Let's try another route.

1. World X is possible & World X is not actual (you would agree)

2. World X is impossible & World X is not actual (obvious)

I give you world Z which is not actual. That is to say,

3. World Z is not actual.

Question for you: Is world Z impossible or is world Z possible?

How would you be able to tell?

How can modal logic (about possibilities and necessities) ever even claim there is only one actual world. — TheMadFool

It doesn't. Rather, the folk in each world think their worlds is the actual world. Third time I've said it.

Question for you: Is world Z impossible or is world Z possible? — TheMadFool

Might be either. You haven't yet specified.

How would you be able to tell? — TheMadFool

When I said Jack might have been a ginger, I specified the nature of a possible world - one in which Jack was a ginger. SO, go ahead and decide if Z is possible or impossible by specifying what's special about it.

It doesn't. Rather, the folk in each world think their worlds is the actual world. Third time I've said it. — Banno

I suppose we might specify a possible world such that the folk therein believe their world is not the actual world.

A world of mad fools?

Might be either. You haven't yet specified. — Banno

You had to come up with the solution.

You had to come up with the solution. — TheMadFool

It's what I do.

Nuh. Jack - a rigid designator - might have been ginger. That sentence makes sense. It's exactly the sort of thing modal logic is intended to deal with.

Jack's identity is maintained across possible worlds. — Banno

It's nothing but a fantasy. If it gives you pleasure to imagine you are thinking something coherent when you say that your cat could have been different than he is,. I suppose there's little harm in it.

I suppose we might specify a possible world such that the folk therein believe their world is not the actual world.

A world of mad fools? — Banno

:chin:

It's what I do. — Banno

So? Where's your solution?

Don't... I shouldn't have...

Stop while you are ahead.

Where's your solution? — TheMadFool

What's the problem?

@TheMadFool

↪TheMadFool The problem with this argument is that the idea of God is not that he could exist in some possible world, but that insofar he could be said to exist in any world then he necessarily exists in every possible world. But that, being a mere idea, doesn't tell us anything about God actually existing. This argument fails in the same way as the Ontological Argument. — Janus

:up:

It's nothing but a fantasy. — Janus

One I share with most modal logicians and others since Kripke.

But I think we've had this conversation before? Have you forgotten, again?

What's the problem? — Banno

1. World X is possible & World X is not actual (you would agree)

2. World X is impossible & World X is not actual (obvious)

I give you world Z which is not actual. That is to say,

3. World Z is not actual.

Question for you: Is world Z impossible or is world Z possible?

How would you be able to tell? — TheMadFool

:up:

Is world Z impossible or is world Z possible? — TheMadFool

Might be either. You haven't yet specified. — Banno

What you suggest is that there is an atomic world where each configuration of a grain of sand in every possible desert is actualised in possible worlds. Clearly not mate. On the other hand there could be a paradox of all these worlds, in a holographic light. Even then, it seems a bit too stark. I would suggest thinking any world is possible, but only those we demand are made.

What you suggest is that there is an atomic world where each configuration of a grain of sand in every possible desert is actualised in possible worlds. Clearly not mate. — Varde

Who you talking too?

Either click on the back arrow at the bottom of a post to reply, or highlight a piece of text in a pst and click on "quote".

Or if all else fails, use a name instead of "You"

theMadFool.

Okay I will do that from now on.

Cheers.

My memory tells me we probably have had a conversation, not identical, but roughly along similar lines as this one before.

:lol:

You seem to think of possible worlds as things we find and investigate, through a microscope or telescope.

They are just stuff we make up. A way of talking about possibilities.

SO, when you tell us more about world Z, we might decide if it is possible or not.

Update

1. If world X is not actual then there's a proof why world X is not actual.

2. If there's a proof that world X is not actual then necessarily world X is not actual.

3. If necessarily world X is not actual then world X is impossible.

4. If world X is not actual then necessarily world X is not actual. (1, 2 HS)

5. If world X is not actual then world X is impossible. (3, 4 HS)

6. If world X is possible then world X is actual. (5 Contra)

Can you have a look $\uparrow$.

1. If world X is not actual then there's a proof why world X is not actual. — TheMadFool

Nuh. The "proof" is just you specifying that X is the actual world or that it isn't.

2. If there's a proof that world X is not actual then necessarily world X is not actual. — TheMadFool

Nuh. The "proof" is just you specifying that X is not the actual world or that it is. But also, the phrase "Necessarily word X is not actual" is ill-formed. It comes out as something like "in all possible worlds world X is not actual"; which presumably is just "World X is impossible".

Try substituting "in all possible worlds" for "necessarily" in your thinking; you may begin to see why the possible world way of talking clears the air. The confusion you are suffering might be because you are mixing two ways of speaking about modality.