In S4 or S5, or a derivative therefrom, can an individual exist in every possible world without contradiction? — Banno

In S5 it seems one can, as I explained to you before. This video is helpful, though a little long (you can skip to 10:50 if you want the short version, but I’d suggest you watch the whole thing):

This kind of logic is founded on philosophy and philosophy can offer very different answers. In my opinion, in philosophy there is nothing contingent or necessary that exists. These are relations of ideas. The world exists neither contingently nor necessarily. It is necessary that the world exist if it is existing but this doesn't mean it had to exist a priori or that it is contingent a priori such that it needs a necessary substance or whatever to back it up. The proper distinction in mind and world situations is "objective vs subjective". Subjective is fooling or lying to oneself. Objective is what is real towards consciousness. As Kant, Hegel, and others point out, the world is there and we don't create it but turn over the coin and we see that we don't know how much we might be contributing to creating the world, and modern psychology backs this up to a great extent

Well, I was looking for a second opinion. And further I don't see where my actual question was addressed.

I'm not impressed. That post looks like hand-waving.

Then how does modal logic apply to reality. It's concepts are necessity and contingency, neither of which can be proven to apply to the world the way they do to ideas

The concepts apply to propositions, or formally - sentences, including propositions about the world.

In mathematics, salient uses of modality include analysis of provability ('The Logic Of Provability' - Boolos) and for semantcs for constructive logic.

The desk across the room is contingent because it can be destroyed and I will of necessity die if hit by a train. That is science, not logic. Modal logic is a waste of time because philosophy easily shows it's bs. Again it's use is for science, not philosophy

"The desk across the room" is a noun phrase, not a proposition. The modal operators are applied to propositions not noun phrases.

Would you please tell me what textbook in modal logic is the basis of whatever familiarity you have with the subject?

Wikipedia and it's application in articles. Modal Logic is a structural thing and when it says a proposition is necessary or contingent, this is not using the word as it is used in traditional philosophy but this doesn't stop people from pretending it does. Why not show us something unique model logic had proven

You are just providing more reasons to ignore your posts.

Wikipedia and it's application in articles. — Gregory

Wikipedia and those articles don't mention that the operators are applied to sentences and don't refrain from saying that the operators are applied to "ideas" or noun phrases?

You don't like philosophy any

I was explaining how necessity and contingency are used in traditional philosophy and model logic in totally different ways

this is not using the word as it is used in traditional philosophy — Gregory

Do you have a problem with Aristotle's "traditional philosophy"?

I was explaining how necessity and contingency are used in traditional philosophy and model logic in totally different ways — Gregory

Whatever you thought you were explaining, you did it by terribly misunderstanding the modal operators in modal logic, thus giving reason to think you don't know anything about modal logic.

You don't like philosophy any — Gregory

Good be sentences.

What you call classical philosophy was a hodgepodge when it came to modality. The work in modality has given us a syntax within which we can construct a coherent account.

And no, you have not given an account of classical modality. You've done nothing more than make an accusation.

But, hey, you've provided a reason for the thread to appear towards the top of the main page, so that's positive. It might attract someone who can address the OP.

Aristotle is fine but logic is subjective though necessary and doesn't apply in reality. Modal logic is not a philosophically traditional way of thinking. What do you know of Hegel's logic btw

Before you present any model logic you have to prove logic can prove something outside the mind. Can you provide an example? I searched "what had model logic proved" and there was nothing

Read Kripke.

If Aristotle is fine with you, then what particular break between Aristotle and modern modal logic do you object to?

Modal logic is not a philosophically traditional way of thinking. — Gregory

That depends on a definition of "philosophical traditional way of thinking" and its import depends on whether it is important to adhere to "philosophically traditional ways of thinking".

What do you know of Hegel's logic — Gregory

I haven't made any claims about Hegel's logic.

I searched "what had model logic proved" and there was nothing — Gregory

https://philosophy.stackexchange.com/questions/23929/what-are-the-practical-applications-of-modal-logic

https://www.sciencedirect.com/science/article/pii/S1571066114000905

Well, I was looking for a second opinion. And further I don't see where my actual question was addressed. — Banno

Well, I only quoted your first question, and was waiting for somebody else to answer the second one.

As to that second question:

In predict calculus we might cheat and represent that an individual exists as ∃(x)(a=x); is there some way to pars this into modal logic, such that the individual (a) is in every possible world? — Banno

Well, that question just leads to: Does the idea of a being who exists in all possible worlds involve a contradiction? So it just goes back to the first one.

If you could elaborate on what you think entails a contradiction about the idea of such a being (or why it would be illformed) I or somebody else could give you a clear answer, otherwise the question might be a bit too broad.

It's your thread but I'm not your student

Aristotle would not have supported proving anything exists simply from logic structures alone. There are pure Platonic ideas which logic can't touch and the real practical world of reality.

I only quoted your first question, — Amalac

B applies to a theorem, not an individual. I don't think we have an answer yet.

Is ▢ ∃(x)(a=x) well-formed? Is it a theorem of S5?

There is no need to study logic at all if one can get through and understand Hegel's book on logic

I don't know if I should laugh or cry.

I didn't say you don't try at philosophy but you've had many discussions with me and to my brain you put things in neat packages. Socrates at the start had a fluid way at coming to truth (as he saw it). Why would you ask logic to tell you if you could exist in every world? To me it sounds strange

Logic is just grammar, just syntax. It sets out what we can consistently say. So if you would be consistent, you ought understand logic.

And it has advanced greatly since Aristotle.

Ok, well I learn something every day. There might be some of that which would register with me.

Cheers.