nature. He employs methods of exclusion, and aims at an absolutely certain result. Such and such a form is present where no heat is, is absent where heat is, varies without a corresponding variation of heat—therefore that form is not the form of heat. It is excluded. So with other forms. But there is a limited number of forms, i.e., of principles of corpuscular structure. Now heat in omnimoda materia et subjecto susceptibili[1] has, ultimately, but one form, which alone remains as the cause of heat. All the others have been excluded.
It is obvious that the Method of Exclusions is inapplicable unless we are acquainted with all possible forms. How we are to attain such a knowledge Bacon has not succeeded in showing us, any more than he has succeeded in showing us how to attain a knowledge of all possible simple natures clearly defined.
Be that as it may, it is sufficient for our purpose to point out that the Baconian method of induction is not essentially distinct from the Aristotelian. Aristotle's second type of induction proceeds upon the principle of complete enumeration, and consequently involves complete exclusion also. Bacon's method proceeds upon the principle of complete exclusion. In Aristotle there is an exhaustion of positive instances, in Bacon there is an exhaustion of negative instances. In both absolute certainty of induction was the aim.
And the positive instances of Aristotle and the negative instances of Bacon are both referable to form. For Aristotle's Inductive Syllogism it is necessary to exhaust types or species. And, in Aristotelian metaphysics, types or species are forms. The Baconian inductive method proceeds by excluding all forms but one, which is the form of the simple nature investigated. The same difficulties attach to both Aristotle's Inductive Syllogism and the Baconian inductive method. It does not seem possible at any time to divide nature into a fixed number of forms, as both methods require. Knowledge is dynamic and further forms may be discovered. Bacon, perhaps, implicitly recognised this possibility. "Jam vero tempus est, ut artem ipsam interpretandi naturam proponamus ... tamen necessitatem ei abso-
- ↑ Op. cit., II, 17.
