Thank you for your question. It is not exactly clear to me what sorts of things you are concerned about. Is it about expressing things verbally, or is it defining words or phrases? Your question touches on both issues. However, I'll first just discuss the issue of defining words and phrases. For the case you do raise, namely 'art', there has indeed been a lot of reflection about whether that term can be defined. This was much discussed in the middle of the last century in the field of aesthetics. The topic does still get some attention, and one thing we now see is that it's by no means clear that 'art' cannot be defined. In fact, a number of highly original and insightful contemporary philosophers (including Jerry Levinson, George Dickie and Stephen Davies) have forwarded definitions of art that have something going for them. I suspect that if you studied these theories you'd be at least *open* to the possibility that 'art' can be defined after all. So when you ask whether we lack the ability to define words like 'art', I'd suggest that it's not clear that we do lack that ability.

The larger issue your question points to, however, seems to be this: Are some terms indefinable, and if so, why? I think a consensus among philosophers is that some concepts are not definable, but that it's not clear why this should be a bad thing. After all, just as all explanations depend on unexplained primitives, so too do all definitions. (In geometry, for instance, you have to take something as primitive, such as the notion of a point.) So it's just the way definitions work that implies that some things are indefinable, but it's not clear why this should be a cause for concern. It's not due to ambiguity, nor to linguistics. It's even misleading to say it's due to human limitations, as if some other species might do better. Rather, it's due to the nature of explanation.

This of course does *does* not mean what we shouldn't try to explain as much as we can. It does mean--to borrow an image from Wittgenstein--that eventually our shovel is going to hit bedrock.

Mitch Green