[p] 15. The different writers on the Law of Nations disagree widely with
regard to kinds and numbers of sources of this law. The fact is that the
term "source of law" is made use of in different meanings by the
different writers on International Law, as on law in general. It seems
to me that most writers confound the conception of "source" with that of
"cause," and through this mistake come to a standpoint from which
certain factors which influence the growth of International Law appear
as sources of rules of the Law of Nations. This mistake can be avoided
by going back to the meaning of the term "source" in general. Source
means a spring or well, and has to be defined as the rising from the
ground of a stream of water. When we see a stream of water and want to
know whence it comes, we follow the stream upwards until we come to the
spot where it rises naturally from the ground. On that spot, we say, is
the source of the stream of water. We know very well that this source is
not the cause of the existence of the stream of water. Source signifies
only the natural rising of water from a certain spot of the ground,
whatever natural causes there may be for that rising. If we apply the
conception of source in this meaning to the term "source of law," the
confusion of source with cause cannot arise. Just as we see streams of
water running over the surface of the earth, so we see, as it were,
streams of rules running over the area of law. And if we want to know
whence these rules come, we have to follow these streams upwards until
we come to their beginning. Where we find that such rules rise into
existence, there is the source of them. Of course, rules of law do not
rise from a spot on the ground as water does; they rise from facts in
the historical development of a community. Thus in Great Britain a good
many rules of law rise every year from Acts of Parliament. "Source of
Law" is therefore the name for an historical fact out of which rules of
conduct rise into existence and legal force.