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that we study in the doctrine of multitude. It is on the
contrary a branch of logic which, like all
logic, is directly dependent upon mathematics.

The first question we come upon in
the study of multitude is very obviously a
purely logical question; and there is nothing
at all corresponding to it in the doctrine of ordinal
numbers: it is the question what is multitude.
Multitude is obviously a relative quality
of collections, or plurals. Therefore the question becomes,
What is a collection? That is obviously a
most important question for logic; and it is
about as difficult a one as could be found.
In speaking of a collection, we
do not mean that its members are physically