2. Classification and hypothesis bring us into Deduction, which is not really a separate kind of inference from Induction, but is a name given to science when it becomes systematic, so that it goes from the whole to the parts, and not from the parts to the whole. In Induction you are finding out the system piecemeal, in Deduction you already have the clue; but the system, and the system only, is the ground of inference in both. Induction is tentative because we do not know the system completely. Their relation may be fairly represented by the relation of the first figure of the Syllogism to the second and third. The difference is merely that in deduction we are sure of having knowledge which covers the whole system. If a man observed, “The difference {163} between the dark blood in the veins and the bright blood in the arteries calls for explanation,” that is the beginning of Induction. If a man states the circulation of the blood as an explanation, that is Deduction. Really Induction is only a popular name for such Inference as deals with numbers of instances. Mill’s experimental methods do not depend upon number of instances, but only upon content; they presuppose the instances already broken up into conditions A, B, C, and consequents a, b, c.
I must distinguish subsumption and construction as two forms of deduction. Only the former properly employs Syllogism in the first figure.
Subsumption
(a) Subsumption is argument by subject and attribute; i.e. when we do not know the system so as to construct the detail,—e.g. a man’s character,—and can only state in what individual system the details occur. Then we really want the major premise to lay down the properties of the system, and all deduction can therefore be employed with a major premise, e.g. a mathematical argument might ultimately take the form, “space is such that two parallels cannot meet.”
Construction
But (b) when the nature of the subject is very obvious, and the combinations in it very definite, then the major premise is superfluous, and adds nothing to the elements of the combination.
“A to right of B, B to right of C.
∴ A to right of C.”
This is clear, but it is not formal; as a syllogism it has four terms. It is simply a construction in a series of which the nature is obvious. And if you insert a major premise it would be, “What is to the right of anything is to the right {164} of that which the former is to the right of,” and that is simply the nature of the series implied in the inference stated in an abstract form. “Inference is a construction followed by an intuition.” [1] The construction, I think, however, must be a stage of the intuition. I am therefore inclined to suggest that a factor of general insight into principle is neglected in this definition, from which much may undoubtedly be learned.
[1] Bradley, Principles of Logic, p. 235.
Causation