These two questions raise an issue that is related to my earlier
notes about simplifying and clarifying the foundations of ontology. (01)
One of the points I emphasized in my 1984 CS book and keep talking
about in various ways is the distinction between what I called
a *natural* type and a *role* type: (02)
- A natural type is specified by a monadic predicate that describes
or characterizes the essence of some entity or kind of entity. (03)
- A role type is specified by a monadic predicate that describes
how some entity is being used or perceived. It describes a *role*
that the entity plays with respect to something external to itself. (04)
This distinction is based on the notion of *essence*, which is
an ancient term that has been criticized by various philosophers,
notably Willard Van Orman Quine. Nonetheless, it is still useful,
even though it might not be as absolute as some people had hoped. (05)
From Aristotle to the present, the prime examples of natural types
(or natural kinds) are the biological species. Aristotle's term
for them is *ousia* (usually translated 'substantia' in Latin and
'substance' in English). (06)
But the word 'substance' in English has acquired other meanings that
tend to create confusion. Therefore, I don't recommend it as a term
for teaching an intro to ontology (except in historical references). (07)
In any case, the *substantial form* that determines the essence
of a biological species can be identified with (or at least put in
a one-to-one association with) the DNA that characterizes the species.
But this creates problems with "genetically engineered" plants and
animals. (That's a point that Quine did not mention, but he would
have, if it had been more common in the 20th century.) (08)
For anything other than biological species, the terms 'natural kind',
or 'natural type' are harder to define. But the monadic predicates
that specify entities according to something that might be called their
"nature" or "form" are more fundamental than predicates that describe
them according to some use or role with respect to anything external. (09)
The distinction between natural and role types can also be extended
to different kinds of information. The word 'proposition', for example,
is more fundamental than the words 'assertion', 'statement', 'judgment',
'assumption', 'belief', 'hypothesis', 'axiom', or 'theorem'. Therefore,
it is reasonable to say that Proposition is the natural type, and the
other words describe roles that a proposition can play. (010)
The words 'datum' and 'data' most definitely describe roles. Even
their etymology indicates that: 'datum' is the singular, and 'data'
is the plural past participle of the word 'dare' in Latin, which
means 'to give'. (011)
In short, whatever you are given is data. That is the role.
The natural type or types of what is given are totally unknown.
Some databases include descriptors that can specify types, but
some don't. And many databases are sufficiently general to store
anything and everything that can be processed by a digital computer. (012)
Recommendation: When trying to classify anything that is described
by a term t, ask how the word t is defined. If it specifies something
according to its characteristic nature or form, it is a candidate for
a natural type. But if it describes something according to its use or
role with respect to something outside of itself, it is a role type. (013)
John (014)
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