... and therefore not established by "essence" or "necessity," as you had formerly claimed. Now we're getting somewhere.

So the remaining question is: What exactly is the convenience or purpose that this distinction serves?

I'm genuinely interested in your answer to this question. What important thing does this distinction preserve? What would be lost if we simply merged the Philosophy and literature sections of the book store (renaming the section "Speculation," if you like?)

You've heard my theory about this question. The traditional, artificial distinction exists to "protect" philosophy -- to maintain the illusion that it is uncontaminated by the tools by which fiction seeks the Truth (if and when it does so) -- the tools of metaphor, analogy, embedded trope, etc., used by all philosophy, without exception; to maintain the illusion that philosophy is "closer" to truth than literature.

Chess is a convention (not found in nature) but it is a necessary truth that in chess the king is checkmated iff it is in check, but has no legal move. Why can't there be necessary truths concerning conventions? So, you seem to be mistaken about that. Would you say that physics claims to be closer to the truth than literature. Or, would you object to that, too?

Oh yes, philosophy does use analogy and so on. But that is not of its essence, and it need not. It is of the essence of literature to do that.

And literature does not pretend to give us knowledge (except in some metaphorical way). Philosophy does (or rather, should).

We seem to have gone afield of the original assertion:
It seems pretty clear you had more than "convention" in mind here.

It doesn't matter, though, since it's not true in any case. There is no level at which philosophy somehow gets beyond trope and metaphor. These are embedded just as deeply in its discourse as it is in any literary text.

Really? What does it mean to say that The Symposium, for instance, gives us "knowledge," but War and Peace does not?

In what way is War and Peace reliant on metaphor, but The Symposium is not? One could easily argue that the latter makes much greater and more frequent use of metaphor than the former.

The only reason philosophy tends to brand literature as "metaphor" -- as if philosophy is not equally constituted by it -- is to suggest, falsely, that literature is at a greater "remove" from reality and truth.

How can your favourite philosopher not be yourself?!

To begin with, you may not be a philosopher.

What does it mean to say that The Symposium, for instance, gives us "knowledge," but War and Peace does not?

Of course, the Symposium is a particularly good case for your position, since it is a particularly literary example of philosophy.

There is obviously overlapping.

Why don't you try, instead, contrasting Locke's Essay on Human Understanding or Quine's Word and Object with War and Peace.

I like Max Stirner, because he understand the all value comes from individual person. Nobody else do that, they all talk about 'duty' or 'humanity' or something like that.

I also like Ludwig von Mises, who economist but say thing very close to what Stirner says.

? I picked it because it is a work that is considered to represent the quintessence of philosophy, if any single work does. It isn't insignificant that your argument requires that this bedrock of philosophy be avoided in favor of peculiar, carefully selected examples -- peculiar both historically and generically. A motion that is all the more telling in that you wanted to make an assertion about an essential and necessary difference (your words) between philosophy and literature.

... a figure that presumes, again, that there is an essential "center" to philosophy and to literature that are absolutely distinct. If the Symposium does not partake of that center, then nothing does.

But just for fun, let's take the carefully selected examples you require -- carefully selected, but at the same time forwarded as the respective centers of the "overlapping" circumferences of philosophy and literature:

ok, let's try them. What does it mean to suggest that Locke gives us "knowledge," but Tolstoy does not?

To begin with, you may not be a philosopher.

Who considers the Symposium the quintessence of philosophy?

It is clear that Locke is trying to inform us about matters like, whether there are innate ideas, the nature of perception, and so on. Tolstoy is relating a great swath of history from the point of view of a few key characters. It is like the difference between chalk and cheese.

No one discusses War and Peace in a philosophy class, but Locke's Essay is often discussed in philosophy classes. On the other hand, the novel is discussed in 19th century literature classes, but Locke's Essay is not in any literature class.

I said it is considered to be, if anything is. You know I don't put stock in that kind of essentialism myself; and you know that I'm only going along with the categories of essence and necessity that you introduced, to explore the question.

Most Classics scholars would agree that if there are essential or central philosophical texts -- as your "overlapping" figure suggests -- then the Symposium certainly would have to be among them.

You have cited a couple of subjects that Locke is "trying to inform us about." I can cite several such subjects that Tolstoy is trying to inform us about -- some metaphysical, some ethical. I still don't understand why Locke can be said to traffic in "knowledge," but Tolstoy not.

Surely you agree that this simply begs the question. If we were to argue about whether there is an essential and necessary distinction between Cheddar and Cream Cheese, it makes little sense to cite the fact that the grocery store keeps them separate. It's the tail wagging the dog...

The mere fact that institutional structures usually follow a convention of keeping the names of these disciplines distinct -- although they don't always do so, and neither is it true that the texts we've been discussing are rigorously kept out of each others' classrooms -- does not explain the principle by which philosophy and literature can be said to have distinct essences or centers.

Most Classics scholars would agree ......

Some classics scholars do, but most don't, know a lot about philosophy, and usually, not much about anything but Greek philosophy.

The question is whether what Tolstoy is informing us about is philosophy.

That's fine. Substitute any of Plato's texts that you wish. Does it change anything?

In any case, I guess we'll have to leave it to others to judge this conclusion, that Plato's Symposium is considered by most scholars to be literature and not philosophy.

Ah, pardon me, but this is precisely not the question -- not least because it assumes that the "essence" of philosophy has already, somewhere, been defined.

It is exactly that definition that we've been after, right? And it was to this end that you provided the formula that philosophy conveys knowledge, whereas literature does not.

That's been the repeated question all along. What is the knowledge that philosophy conveys that literature does not?

Good, how about the Theaetetus? That is clearly a work of philosophy. It is about knowledge. No one would ever call it a work of literature.

The knowledge that philosophy is about is conceptual knowledge. Knowledge about the fundamental concepts of thought and language.

Actually, I would rather say that philosophy is about understanding than knowledge. Science is about knowledge. Philosophy is about understanding. Literature is about entertainment.

Someone like Derrida is about confusion.

Yes, let's take it. And I can't help but note in passing that we have been required to do so by your remarkable contention that the Symposium, at its center, is without question not philosophy...

The very first thing the reader will notice about the Theatetus -- which you're forwarding as the work in Plato's corpus that is the purest philosophy, freest from the taint of literature -- is that it is... a work of fiction. It dramatizes a relationship and a dialogue among fictional characters. It does so for the purpose of elucidating questions of knowledge and judgment, among other things -- and it does so almost entirely through the use of analogies, extended metaphors, and even further fictional scenarios. (Fictions within fictions... It's got the narrative complexity of something by Conrad!)

For myself, I can't see any significant difference between these strategies of rhetoric and storytelling and those found in the novels of Musil, Dostoyevsky, Kundera and Coetzee, for precisely the same object of elucidating questions of knowledge, judgment and ethics.

Ever read Kafka? Borges? Cervantes? Stoppard? Beckett? Poe? Melville? You may be surprised...

Again... you're confusing your personal dismissal of literature as "mere entertainment" -- and I'm not sure who in the world would characterize, say, The Brothers Karamazov or Paradise Lost in this way -- with the essential "center" that constitutes literature, but whose existence we still can't seem to verify...
I wouldn't mind discussing this; but you have so studiously avoided backing up such hit-and-run zingers that I can only let it pass with the same patient smile I have to give students when they insist a book must be nonsense because they can't understand it. If you'd like a primer of Derrida and poststructuralism in general, I really do recommend (shamelessly) my recent video on the subject. (Or if you prefer YouTube: YouTube - BrianArtese's Channel)