Ontology notes: What's a "thing"?

Conceptual ontology has been an interest of mine since graduate school. Many ontologies will start with "thing" at the root of the ontology, which seems logical enough. After all, isn't everything some kind of thing? Here's a note I wrote to Language Log's Mark Liberman a decade or so ago:

Dear Mark Liberman,

I few days ago I happened upon "Language Log" and, in particular, I read some of your snippits on ontology. In one of them you assert:

"There's an interesting question to be asked about why people persist in assuming that the world is generally linnaean -- why mostly-hierarchical ontologies are so stubbornly popular -- in the face of several thousand years of small successes and large failures. I have a theory about this, which this post is too short to contain :-) ... It has to do with evolutionary psychology and the advantage of linnaean ontologies for natural kinds -- that's for another post."

Evpsych aside, there's something peculiar going on. From an informatic point of view, the nice thing about linaean structures is that they allow for relatively compact "storage" of information because they allow for inheritance.[1] If you don't know that dogs, cats, rats, and cattle are all mammals, then you've got to store their common features (e.g. general body plan) separately for each. If you know, however, that they are all mammals, then you can store the common features with mammal and allow those features to be inherited by each type of mammal.

But there's something else going on. Language has words for very general classes of things, such as objects, events, attributes, states, and most general of all, things. Whatever else something might be, it is, most assuredly, a thing. So it becomes easy and tempting to start a hierarchy with "thing" at the root and then basic kinds of thing one level down, e.g. "object," "event," "state," and "attribute." Then we might start on the next level and have, say, physical and abstract objects, and physical and abstract events, and physical and abstract . . . And this is beginning to look rather strange.

But what kind of inheritance do we have in this kind of structure? What is it that objects, events, attributes, and states inherit from thing other than thinghood? What is it that physical and abstract objects inherent from objects other than objecthood? Somewhere down there we're going to come to "living thing" and then we can have linnean inheritance from there down. But it's not at all clear to me what's going on between that point and "thing" up there at the root of the tree.

It's a most curious business.

My dictionary informs me that it is "Old English, of Germanic origin; related to German Ding. Early senses included ‘meeting’ and ‘matter, concern’ as well as ‘inanimate object’."And beyond that?

It almost feels like a grammatical function or capability has been turned into a noun and given a name. What is a thing? Well if it can play certain roles in sentences, then it's a thing. As a grammatical category we refer to it as a noun, as an object or phenomenon in the world we refer to it as a thing.

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[1] Though I don't have the text in front of me at the moment, I recall that somewhere in The Order of Things Foucault talks about how informatic inheritance was one reason for creating linnean taxonomic trees.