INDUCTION, the name for one of the great processes of scientific discovery proof. It has been seen under GEXERALIZATION, that when we rise from particular facts to generalities, the result may take one of two forms—a general notion, or a gen eral proposition: " circle " is a notion; "the circle is the line that Meioses the largest, space," is a proposition. The mode of arriving at such general affirmations, truths, or laws, is what is called induction. The strict meaning of the term is "the operation of. discovering and proving general propositions;" while deduction, on the other hand, is the method of applying general propositiohs once discovered to particular cases, considered. to be included within their scope. By induction we establish the law that heat expands bodies; by deduction we apply it to explain why a clock is slower in summer than in winter, owing to the changes of the length of the•pendulnin.
Induction is the Only proceSS of real inferened—In other words, by it we proceed from the known to the unknown; or from a limited range of facts, we affirm what will hold in an unlimited range. All things that we do not know by actual trial or ocular demonstration, we know by an inductive operation. Deduction is not real inference in this sense, since the general proposition already covers the case that we apply it to; in a proper deduction, the conclusion is more limited than the premises. By the inductive method, we obtain a conclusion much larger than the premises; we adventure into the sphere of the unknown, and pronounce upon what we have not yet seen. This opera tion necessarily implies a certain hazard; and it may be easily supposed that there are 'precautions requisite in working it. Nothing is more common than the making of bad inductions; and accordingly it is now considered a part of logic to lay down the rules for the right performance of this great operation.
A preliminary question arises—How can we ever be entitled to dogmatise beyond the sphere of our actual experience; to conclude, for instance, that five miles below the surface of the earth there is heat enough to make water boil? The answer to this ques tion supplies us with what is called the ground of induction, which is the fact, now established by the experience of centuries, that nature is uniform. What has happened
once, will happen again, provided the same circumstances and situation of things are exactly repeated. At a former period of the world's history, there might have been doubts on this matter, and opinions were actually held that implied a want of perfect uniformity, but now those doubts are dispelled, except, perhaps, with reference to a single question—viz., the freedom of the will (see 'FREE WILL). Accordingly, the problem to be solved is to ascertain what is the order of nature in the instances accessi ble to our observation.
The uniformity of nature is a compound of many separate uniformities. In other words, there are different departments or classes of phenomena, each determined by separate laws. Thus, we have mathematical, physical, chemical, physiological laws, the statement of which severally constitutes the subject-matter of each of these sciences. Now, a distinction is observable, which is of some-importance as regards the method of inductive investigation, Some of the phenomena thus conjoined under uniform prin ciples are properties simultaneously existing, as the properties of mathematical figures; others are successions, and affirm order in time, the most important of all which is that peculiar succession denominated cause and effect. See CAUSE. The problem of induct ive inquiry is in a great measure occupied with this one department, although there are also inductions respecting contemporaneous or conjoined .properties. Natural his tory is in part made up of affirmations of simultaneous properties, as, for example, the anatomical structure of animals, and in part of affirmations of cause and effect, as in all the operations that sustain life, and determine reproduction, growth, and death.