Jejudo, South Korea
Existence as a concept is the problem; it's very ambiguity causes a lot of problems because it's so related to discussion of Being and beings and whatnot -- a lot of discussion has been generated by attempting to find the common 'nature' as Stephan put it to things that exist. In order to do that, of course, you have to counterpose something that doesn't exist -- otherwise, we'd have an undifferentiated esistence.
As far as I can tell, most of these discussions presuppose a difference between concepts and reality sans concepts and the ambiguity surfaces when someone tries to integrate mental concepts back into that same reality. The other problem is a lot of people seem to jump back and forth between relational existence and absolute existence.
Take a horse for example. If I see a horse, feel it, touch it, feed it etc., I can say the horse exists, but as I look out my window right now, I see no horse, so I can say that no horse exists there, now. The reply is usually something like, "Yeah, but there are still horses. Horses exist," and that is indeed true, but it's a shift in context and irrelevant to whether a horse exists there, now.
But take a unicorn in contrast. As far as we know, no unicorns have ever been known to exist in that there, now in the same sense that a horse can indeed exist in that there, now (but not outside my window there, now). Thus, we say unicorns don't exist. Perhaps we can make that clearer by saying that unicorns don't exist in the same way that horses exist.
The response then is usually something like, "Yeah, but we have a concept of a horse and we have a concept of a unicorn. There both concepts and concepts exist, therefore, they both exist" but this is a mistake, for it forgets the difference between the two concepts. The concept horse includes the ability for a horse to be there,now (and not there,not now) whereas a the concept unicorn does not. Historically, it might have been different, but it's not today:
"There's no unicorn there now," already presupposes the ability to be there, now.
But this doesn't answer all the questions that questions of existence and Being bring up -- it's a tough nut to crack and, perhaps, a psuedo-problem created by a tendency to confuse adjectives with nouns.
I don't know.
[This message has been edited by Brad (09-05-2003 10:02 PM).]