the
method of agreement, especially in the larger theories in biology and
geology, where the lapse of unnumbered centuries is necessary to bring
about changes. In physics, in chemistry, in medicine, on the other hand,
critical experiments are generally possible, and so progress is by the
method of difference. In such subjects as political science and
government, where experiment is out of the question, one must depend
chiefly on the method of agreement, except in such cases as will be
mentioned below where a change in policy has the same effect as an
experiment. Here, however, one must not forget that in all matters human
the incalculable clement of human nature enters to complicate all
results, and that emotion and feeling are always irrational.

It is by the same processes that we get most of our explanations of the
world as we go through it, and most of the facts on which we base
judgment and action. When the same sort of thing happens in a number of
fairly different cases, we begin to suspect that there is a reason; and
if we are going to make an argument on the subject, we take note of the
cases and try in some way to arrange and tabulate them. The supporters
of a protective tariff collect instances of prosperity under such a
tariff, the supporters of free trade cases of prosperity under free
trade, the believers in the classical education cases of men trained in
that way who have attained to eminence, believers in the elective system
cases of men who are the products of that system who have attained equal
eminence. In most cases such collection of instances does not carry you
far toward a coercive argument; the cases are too complex for you to
assert that any one factor is the cause of the result.

In another kind of case you can come a little nearer. In an argument for
the establishment of a commission form of government in a given city or
town there are now enough cases of this type of government in practice
to make possible a good argument by the method of agreement; the places
are scattered over the country, north and south, east and west, and
range greatly in size and environments; and all of them so far (1911)
report improvement in efficiency and honesty of government. Accordingly
it is a fair presumption that the improvement is due to the introduction
of the new form of government, since in all other respects the places
which have tried it have little in common.

A more important result of the inquiry is