of law, is not only allowable but
obligatory.

A second assumption must be that there is a unity of kind and purpose in
all religions. Without this, no common law can exist for them. Such a
law must hold good in all ages, in every condition of society, and in
each instance. Hence those who explain religious systems as forms of
government, or as systems of ethics, or as misconceived history, or as
theories of natural philosophy, must be prepared to make their view good
when it is universally applied, or else renounce the possibility of a
Science of Religion; while those who would except their own system from
what they grant is the law of all others, violate the principles of
investigation and thereby the canons of truth.

The methods of science are everywhere alike. Has the naturalist to
explain an organism, he begins with its elements or proximate principles
as obtained by analysis; he thence passes to the tissues and fluids
which compose its members; these he considers first in a state of
repose, their structure and their connections; then he examines their
functions, the laws of their growth and action; and finally he has
recourse to the doctrine of relations, _la theorie des milieux_, to
define the conditions of its existence. Were such a method applied to a
religion, it would lead us first to study its psychological elements,
then the various expressions in word and act to which these give
occasion, next the record of its growth and decay, and finally from
these to gather the circumstantials of human life and culture which led
to its historic existence.

Some have urged that such a method should not be summoned to questions
in mental philosophy. To do so, say they, is to confound things
distinct, requiring distinct plans of study. Such a criticism might have
had weight in the days when the mind was supposed to inhabit the body as
a tenant a house, and have no relation to it other than that of a casual
occupant. But that opinion is antiquated. More than three-fourths of a
century ago the far-seeing thinker, Wilhelm von Humboldt, laid down the
maxim that the phenomena of mind and matter obey laws identical in
kind;[6-1] and a recent historian of science sums up the result of the
latest research in these words:

"The old dualism of mind and body, which for centuries struggled in vain
for reconciliation, finds it now, not indeed in the unity of substance,
but in the unity of laws."[6-2]

It is, therefore, as a qu