This is my point: ANYTHING that is the subject of discussion in a domain is a THING in that domain.  One thing, and not another.  That is what we need to care about: what people CAST as things, not what are "really" things.

The categories they use, in their domain, are the types or classes or concepts or whatever you want to call them.  The things **fall into** these categories.

For example, in publishing, a BOOK is a type of thing, but MOBY DICK is a single book, that we can distinquish from all other books.  It has an identifier, etc.  IT (a thing) can be protected by copyright.   It should be treated as a thing, not a type of thing, in a domain ontology for publishing.  (And, it DOES have parts.  They are called chapters.  The chapters have parts, too: titles or numbers, paragraphs.)   Most of what is being said in this forum seems to me be about philosophical and mathematical theories, not about representing the thinking, reasoning, and discourse of people as they engaged in their work.

It seems that some of us distinquish between individuals and things.  That is fine with me, as 'individual" could well be used as a technical term in many of the ways suggested:  (a leaf node in a tree, something with no parts, something that can be identified by physical means, ...) .  But, I can't understand why there could be an ARGUMENT over the meaning of DEFINED term, only about whether it is a good theory.

Wm