Dear Matthew, William, et al.,

I'm traveling now, and my access to email is spotty.  But I'd just like to emphasize the distinction between language and metalanguage.

I believe that the failure to clarify that distinction and observe it consistently is the source of the disagreements.
 
>> On Mon, December 31, 2012 21:14, William Frank wrote:
>> ...
>> But what seems to me to be most fundamentally wrong in this
>> discussion
>>  is the notion that there is a good reason to define 'kind of
>> activity' separately from 'kind of stone' or kind of hope'.

If Activity, Stone, and Hope, are categories (or classes or types) in your ontology, then you only need two metalevel terms:  'instance of' and 'subtype of' (or 'subclass of').

Those terms let you talk about and distinguish instances of Activity, Stone, and Hope from subtypes of Activity, Stone, or Hope.  The ontology itself should *not* have any categories with names like 'kind_of_activity' or 'class_of_activity'.

> MW: In HQDM the definition of kind_of_activity is:
>
> A class_of_activity all of whose members are of the same kind.
>
> This is not circular definition...

I agree that it's not circular.  But it's not just useless, it's worse than useless because it's confusing.

It mixes the names of categories in the ontology with metalevel terms for talking about the ontology.  You can simplify and clarify the ontology by getting rid of both categories:  kind_of_activity and class_of_activity.

> MW: Since class_of_activity includes arbitrary sets of activities, this
> subset is indeed significant, and includes those activities for which we
> are likely to have words, like singing, rather than mere identifiers.

If you want Singing to be a category of your ontology, all you need to say is "Singing is a type of Activity."   If you want to talk about sets of categories, you need a version of logic that lets you do so.  But that option does not require you to add special categories to the ontology itself.

Aristotle made a very clear distinction between his ontology and his logic.  He did not need any categories with names like 'kind_of_XXX'.  For a brief overview, see the slides I presented at SemTech in 2012:

   http://www.jfsowa.com/talks/kdptut.pdf

John

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