If we now compare the two methods, their aptness, function, and
provinces, we shall find, as in an abstract, the history, divisions,
hopes, and limits of human science. The first appears at the beginning,
the second at the end. The first, necessarily, gained ascendancy in
Bacon's time,[423] and now begins to lose it; the second, necessarily,
lost ascendancy in Bacon's time, and now begins to regain it. So that
science, after having passed from the deductive to the experimental
state, is now passing from the experimental to the deductive. Induction
has for its province phenomena which are capable of being decomposed',
and on which we can experiment. Deduction has for its province
indecomposable phenomena, or those on which we cannot experiment. The
first is efficacious in physics, chemistry, zoology, and botany, in the
earlier stages of every science, and also whenever phenomena are but
slightly complicated, within our reach, capable of being modified by
means at our disposal. The second is efficacious in astronomy, in the
higher branches of physics, in physiology, history, in the higher grades
of every science, whenever phenomena are very complicated, as in animal
and social life, or lie beyond our reach, as the motions of the heavenly
bodies and the changes of the atmosphere. When the proper method is not
employed, science is at a stand-still: when it is employed, science
progresses. Here lies the whole secret of its past and its present. If
the physical sciences remained stationary till the time of Bacon, it is
because men used deduction when they should have used induction. If
physiology and the moral sciences are now making slow progress, it is
because we employ induction when deduction should be used. It is by
deduction, and according to physical and chemical laws, that we shall be
enabled to explain physiological phenomena. It is by deduction, and
according to mental laws, that we shall be enabled to explain historical
phenomena.[424] And that which has become the instrument of these two
sciences, it is the object of all the others to employ. All tend to
become deductive, and aim at being summed up in certain general
propositions, from which the rest may be deduced. The less numerous
these propositions are, the more science advances. The fewer
suppositions and postulates a science requires, the more perfect it is
become. Such a reduction is its final condition. Astronomy, acoustics,
optics, present its models; we shall know nature when we shall have
deduced her millions of facts from two or three laws.
I venture to say that the theory which you have just heard is perfect. I
have omitted several of its characteristics, but you have seen enough to
recognize that induction has nowhere been explained in so complete and
precise a manner, with such an abundance of fine and just distinctions,
with such extensive and exact applications, with such a knowledge of the
practical methods and ascertained results of science, with so complete
an exclusion of metaphysical principles and arbitrary suppositions, and
in a spirit more in conformity with the rigorous procedure of modern
experimental science. You asked me just now, what Englishmen have
effected in philosophy; I answer, the theory of Induction. Mill is the
last of that great line of philosophers, which begins at Bacon, and
which, through Hobbes, Newton, Locke, Hume, Herschel, is continued down
to our own times. They have carried our national spirit into philosophy;
they have been positive and practical; they have not soared above facts;
they have not attempted out-of-the-way paths; they have cleared the
human mind of its illusions, presumptions, and fancies. They have
employed it in the only direction in which it can act; they only wished
to mark out and light up the already well-trodden ways of the
progressive sciences. They have not been willing to spend their labor
vainly in other than explored and verified paths; they have aided in the
great modern work, the discovery of applicable laws; they have
contributed, as men of special attainments do, to the increase of man's
power. Can you find many philosophers who have done as much?