|Abstract:||The topic which has been assigned to me, "Classification Today-
Shadow or Substance," might more appropriately have come at the end
of the Institute, rather than the beginning. If I could convince you that
our pursuit of valid classifications was the pursuit of a shadow, there
would be no reason to listen to the papers on the remaining part of the
program. We could all pack up and go home. Hence, I must conclude
that when those who planned this Institute gave me this topic, they assumed
that regardless of what I might say about classification, I would
certainly be unable to demonstrate its ephemeral or shadowy nature
and that I would conclude that classification had substantial value for
librarianship and related information activities.
Confronted with this dilemma, it occurred to me that the way out
for an erstwhile student of logic like myself might be found in the first
instance not in examining the nature of shadows nor the nature of substances,
but in examining the meaning of the connective between them,
namely, the logical operator "or." Most of us, when we think of the
word "or," think of it in the exclusive sense as meaning "either or,"
that is, the word used in this title, "Shadow or Substance," would ordinarily
be interpreted to mean that if classification were substantial
it could not be shadowy, or if it were shadowy, it could not be substantial.
There is, however, another meaning of "or" which is the usual
meaning attributed to it in works of logic, where the "or" is taken as
meaning logical disjunction with reference to propositions and logical
sum with reference to classes. In this sense "or" means "and/or"
rather than "either or." Thus if I say "It will rain tomorrow or I will
stay home," both statements could be true; that is, it might rain tomorrow
and I could still stay home. Similarly, if I say of an item that it is
a member of the class A or B, it could be a member of A, a member
of B, or a member of AB, and the general proposition "X is a member
of A or B" is true in all three cases. This general proposition is only
false when the item is a member of neither A nor B. This logical relation
can be illustrated by the truth table for disjunction at the top of
the following page.