Causal language is particularly adapted to vague, ill-defined phenomena, about which we can assert little but their presence or absence. Accordingly Mill's remaining canons of induc tion deal with such phenomena. The method of agreement argues a causal relation between A and B when two trains of circumstances arc known which begin in A, and have nothing else in common except their termination in B. The method of difference concludes that A causes B if a train of events is known which contains A and ends in B, while a train of events pre cisely similar except in that it does not contain A likewise fails to contain B. The joint method of agreement and difference is what its name would imply. The method of residues is that in which the unexplained parts of a nexus of events are linked up with one another. Not one of these methods is without _grave dangers except in the hands of the scientist with a con crete knowledge of the field where he applies it. The artificial division or antecedent and consequent alike into a jig-saw puzzle of yes and no occurrences is vicious in the extreme.
Induction has been a method of human reasoning from time immemorial, and has especially characterized those centuries since Francis Bacon. Aristotle, who was the first to recognize induction as a scientific method, gave a very scant account of induction other than that by a complete enumeration of instances. Bacon followed him in this excessive restriction of inductive reasoning. The beginning of the
17th century marks a period when the progress of science had forced a consciousness of the inadequacy of the Aristotelian logic upon the world of learning. The accepted theory of de ductive reasoning began to be supplemented in practice by a meth idology, but no approximately adequate treatment of this methodology was de veloped until the middle of the 19th century. In 1840 Whewell (q.v.) published a work in which for the first time due credit was given to the function of imagining and speculation in inductive reasoning. Soon afterward Mill pub lished his 'Logic,) in which he formulated the five methods of inductive research that have already been mentioned, and expressed the theory, also mentioned above, that every in duction in a syllogism with the uniformity of the nature as its major premise. Since the tune of Mill the growth of inductive logic and methodology has been extremely rapid. (See LAW IN SCIENCE AND PHILOSOPHY; LOGIC; MILL, JoHN STunirr). Consult Aristotle, Bacon, F., (Novum Organtun) ;Joseph, H. W. B., 'Introduction to Logic! (Oxford 1906 ; Mill, J. S., 'System of Logic> (London 1843) ; Russell, B. A. W., Our Knowledge of the External World' (Chicago 1914) • Welton, 'Manual of Logic' (Pt. 11, London 1896) ; Whewell, W., Logic' of the InductiveSciences' (London 1840).
Noinnwr WIENER, Editorial Staff of The Americana