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particulars? And this, along with some lesser problems constitutes what is referred to metaphysics as
the Problem of Universals. Ordinary language often overlooks this problem entirely. When you point to
an object and call it a tree, you do not ask yourself how you know it is a tree. Nor do you ask where the
quality of treeness came from, nor why it could not be called something else. Mark Twain deals with
this problem in a very humorous fashion in the diary of Adam and Eve.
Entry in Adam's diary:
Tuesday: Been examining the great waterfall. It is the finest thing on the estate, I think. The new creature
[Eve] calls it Niagara Falls - why, I am sure I do not know. [She] Says it looks like Niagara falls. That
is not a reason, it is mere waywardness and imbecility.
Robert Pirsig also addresses this problem at length in his bestseller Lila. So the deep metaphysical
nature of this problem does not keep it out of popular culture. Nor does it keep it out of information mod-
eling and database design. Yet, people who have never encountered this problem often find it perplexing
in the extreme. Consider the enigmatic question posed earlier - Is a tree a tree because it is a member of
the set of trees? Or is it a member of the set of trees because it is a tree? In more straightforward terms
these questions are an attempt to find out if kind is determined by category membership or if category
membership is determined by kind.
One is tempted to just leave this tricky problem up to philosophers and go on with one's life. However,
the many practical implications of this metaphysical problem force us to confront it. For example, when
an information modeler looks at an application domain he or she sees particulars which are referred
to as entities. These entities are organized into classes called entity classes which are then represented
in the information model. Entity classes are universals. And the problem of getting from specific en-
tity occurrences to the entity classes represented in the information model is no more or less than the
Problem of Universals. Let's say that we have an information model of university registration. Let's
say further that we have an entity class called Student. We can ask - Is a student a student because he
or she is a member of the set of students? Or is a student a member of the set of students because he or
she is a student? And we are right back to the problem as stated earlier. One would think that people in
a university environment would know what a student is. But a few simple questions expose that fallacy
very quickly. Is a part time student the same kind of thing as a full time student? Is a student who has
not signed up for any classes still a student? Is somebody who sits in class and learns but does not pay
tuition still a student? Are alumni auditors considered students? If somebody pays their tuition using
loans that they later default on, does that mean they never were a student? How we get from the par-
ticulars in the world to the groups into which we organize our knowledge is a foundational problem in
information modeling as well as in metaphysics. The next section will explore the opinions of a number
of western philosophers as they tried to grapple with this difficult problem.
A Br Ief hISTor Y of Pro BLeM of un IVer SALS
Plato was the first western philosopher to seriously consider the Problem of Universals. His concern
was that a person could recognize an object, such as a tree, for example, even though there is so much
variation between individual trees. Some trees are very tall and majestic while others are short and
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