Chapter LXXXVIII: Section X: Comparison of the Methods of Induction and Deduction

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?