This is one of those cases where as long as we're clear on what we mean, there's not much of an issue. It would be perfectly in order to say "that creature existed two weeks ago; it was a chrysalis then." It's like saying that you existed lo so many years ago, though you were a toddler at that time. Leaving aside more radical doubts about identity over time, there's no problem with talking this way. If you say "that butterfly existed two weeks ago" and you mean something like "that creature, which is now a butterfly, existed two weeks ago" then there's nothing to worry about. But obviously if you mean "two weeks ago, this butterfly was around, as a butterfly," then you'd be saying something false.

There are more subtler issues that a philosopher might raise, having to do, for instance, with whether the butterfly (or you, for that matter) is present at any one moment (as opposed to being a 4-dimensional being whose time-slices are present at various instants). But that question would come up even if the butterfly had not, as it were, changed at all over the two weeks.

Let's make two initial comments to muddy the waters!

1) Accepting some version of a correspondence theory of truth -- e.g. accepting that a true proposition is made true by the existence of a corresponding fact -- doesn't ipso fact make you a realist in your ontology. It will obviously depend what you think about facts! (You could still be an idealist like Berkeley, and suppose the only facts are ultimately those involving God, other spirits, and their ideas.)

2) Accepting that our knowledge of the world depends on a lot of processing of data by the brain using built-in cognitive mechanisms doesn't make you an anti-realist in epistemology. You could still hold that when those processes are working reliably, they successfully give you epistemic access to facts that obtain independently of you and your cognitive mechanisms.

I'd say that talk of a "correspondence theory of truth", "realism about ontology", "conceptual frameworks", and "epistemological anti-realism" is all far too slippery to be very useful. As often in philosophy, it helps to try to frame the issues that might be bugging you in plain terms, without any such jargon, and certainly without any reference to "isms". Sometimes it turns out that it was the jargon that was tangling your thought, or greasing the slide into confusion: but even if you are left with genuine problems, it will at least be clearer what they are!

Sure. For one thing, nature doesn't care about our arbitrary units. Suppose we have a plank of wood that''s exactly a foot long. Now I define a new unit: a schfoot. Anything one foot long is exactly pi schfeet long. Is there any mystery about things being pi schfeet long?

Also -- since we're setting aside issues about quanta and, I assume, the possibility that space is granular, can't we make sense of something changing length continuously? A twig that's a foot long and growing will pass through an uncountable number of irrational lengths on its way from being a foot long to being two feet long.

As a philosopher working in the classical European tradition, I see the importance of the distinction between being and existence in very different terms from my colleague, Allen Stairs. His claim that “not everyone sees a distinction here” might be true for a certain segment of the 20th century analytic tradition but is certainly not the case if we look at the history of Western philosophy as a whole, for which the distinction between being and existence has been the central metaphysical question. In fact, I would argue that philosophy was born as the attempt to grapple with this very distinction.

During the late 6th century BC, Heraclitus inaugurated "ontology" (the branch of metaphysics dedicated to the study of being) by focusing on the distinction between being and becoming, which roughly corresponds to that between being and existence. This correspondence was already picked up by Plato who, concerning Heraclitus’s flux doctrine, claimed the following: "Heraclitus, I believe, says that all things go and nothing stays, and comparing existents to the flow of a river, he says you could not step twice into the same river." (Cratylus, 402a). In this quote Plato tries to make sense of one of Heraclitus’s most famous fragments: “Of those stepping into rivers staying the same other and other waters flow.” The fragment brings into focus how a river remains the same over time even though the water flowing through it is never the same.

Already with Heraclitus, the distinction between being and existence invokes the epistemological issue of what can be known and how. Even though Heraclitus does not give a full account of the distinct roles performed by sense experience and reason in relation to knowledge, he certainly suggests what has become their classical alignment. While sense experience can ascertain the “existence” of the world, or its becoming, reason can describe its “being,” assumed as its essential, formal, or theoretical underpinning.

Through many variations, digressions, and permutations, the distinction between being and existence becomes once again the focus of discussion with existentialism. Anticipated by the work of Søren Kierkegaard, during the second half of the 19th century, the question regarding how to define being in relation to existence, and existence in relation to being, takes center stage in Being and Time, Martin Heidegger’s magnum opus. In his “Introduction,” Heidegger claims that the tradition has tried to make sense of the distinction between being and existence by approaching it through the wrong lens. In asking, “What is being?” the tradition has made being into just another existing entity, an impossibility given that being is itself the condition for any entity to exist.

This conclusion brings Heidegger to claim that being and existence are not only irreducible to one another but will remain inscrutable if the way of questioning each of them does not undergo a radical change. Instead of asking “What is being?” Heidegger recommends that we start from looking into the only existing entity for whom being is an all-consuming issue. Thus, in order to access being as such, the human being has essentially to question itself. In this sense, after Kierkegaard, before Sartre, and in sharp contrast to the tradition that interprets human existence in terms of rationality, personhood, or spirituality, Heidegger sees it as the only place where being is brought into view.

What fun! And indeed, it turns out that Giovanna picked my birthday to show me the error of my ways! :-)

As it turns out, however, I don't think we actually disagree about anything. Giovanna has pointed out, in effect, that folks in her tradition use these terms to mark out a distinction (or, it seems to me, a set of related distinctions) that folks in my tradition would talk about in different language. Needless to say, that's not a comment on the value of either tradition nor on the importance of the problems.

I'll confess that I don't think I have the differences here fully in view yet, but if I have it right, one distinction marked by the existence/being distinction is the difference between individual things that exist, change, have properties, etc., and the background against which the possibility of such existents makes sense. Existence, on this way of speaking, refers to the existent things, and being to this broader metaphysical background. Giovanna points to the problem of understanding how something that's always changing ( afact about existence) can nonetheless be the same thing over time (an issue about being?). This is certainly a question that analytic philosophers continue to find interesting. The kinds of problems that Plato wrestled with -- the temporal world of physical objects (existence) vs. the eternal realm of forms (being?) seems to be in the mic hre as well, and once again, analytic philosophers recognize this problem. And while I will confess to not being very familiar with Heidegger's distinction between being "present-at-hand" -- as an object for investingation -- and being "ready to hand" -- as something we simply use without the need to theorize -- also is a perfectly worthwhile distinction that anbalytic philosophers would talk about in a rather different vocabulary.

But whether any of this has anything to do with the thought that "being is the state of quality of existing" is still not clear to me.

In any case, as I said, lots of related distinctions about here, though different traditions of how to talk about them.

You need to be careful to distinguish things and ideas here. Is the question about square circles or about the idea of a square circle?

Compare: there are no such things as unicorns. It would plainly be wrong to say that they "neither exist nor don't exist": unicorns definitely don't exist! But the idea of a unicorn exists and seems coherent enough. Indeed, we are tempted to suppose that there could have been things that fitted the idea.

Likewise, there are no such things as round squares. Like unicorns, round squares definitely do not exist. But this time, though we can frame the idea of a round square -- we grasp that something counts as a round square if it is round and a square! -- the idea is a self-contradictory one in the sense that nothing can possibly count as fitting our idea here.

Consider an example from Frege: the direction of the line L is identical to the direction of the line M if and only if L is parallel to M. That's true. But how should we read it? Do we read it as explaining the notion of being parallel in terms of the identity of two abstract objects, i.e. two directions? Or do we take it the other way about, as partially explaining talk about two abstract objects, directions, in terms of the already-understood notion of lines being parallel? There's lots to be said for taking it the second way, as introducing reference to certain abstract objects in terms of something more familiar.

Likewise: the meaning of "gorse" is identical to the meaning of "furze" if and only if "gorse" and "furze" are synonymous. That looks true too. But how should we read it? Do we read it as explaining the notion to synonymy in terms of the identity of two abstract objects, meanings? Or do we take it the other way about, as (hopefully) partially explaining talk about two abstract objects, meanings, in terms of an easier-to-understand notion, the idea of two words being synomymous (something like: functioning the same way). Again, there's lots to be said for taking things the second way, if we are going to talk about meanings-qua-entities at all.

Certainly a Quinean will want to press the case for taking things the second way both times. But then he makes a further move: at least in the second example, he will want to go on to press the claim that, on reflection, the notion of synonymy is actually pretty murky and problematic. So now our supposed explantion of the notion of meanings qua abstract entities is actually, for that reason, not in very good shape after all.

In the questioner's terms, then: it may be that where we do have a genuine sameness we can introduce "intermediary entities", but those entities needn't be doing any explanatory work, but rather are being explained via the sameness-claims. Further, Quine insists that synonymy is in fact not well-behaved enough to be a kosher sameness relation.