straightway understand why this occurs, viz., because it is illuminated by the sun ..."—in other words, a hypothesis is formed. In the first type of Aristotle's induction, hypothesis is again recognised. There, as we saw, an advance is made from some particulars to a universal. The universal extends beyond the particulars. That universal is, therefore, a hypothesis. If there is one thing in particular which distinguishes Aristotle's scientific achievement, it is his powers of classification. This is specially evident in his classification of facts of natural history. Now classification implies hypothesis, several facts more or less unlike being grouped under one idea.
II.
For an understanding of Bacon's inductive method it is necessary to say something at once of what he means by 'simple natures.' These were limited in number, distinct in kind from one another, and ultimate. Every sense-object is reducible to a combination of certain of these simple natures. Just as a limited number of letters go to make up the infinite variety of worlds, so simple natures go to make up the infinite variety of natural, phenomena.
A happy characteristic distinguishing Bacon from Aristotle is the former's sceptical attitude towards popular opinion. Aristotle, indeed, did, as we have already noticed, appreciate the vague and misleading character of popular distinctions, but this appreciation was no essential part of his philosophy as was the exposition of idola part of Bacon's. Consequently Bacon recognises the difficulty of attaining to simple natures defined with scientific accuracy. Meantime they are vague, indistinct, inaccurate notions—idola fori. Bacon promises aids to the attainment of 'bonæ notiones' but this promise he never fulfils.[1]
Closely connected with his use of 'simple natures' is his use of 'forms.' By 'form' Bacon means the particular principle of corpuscular structure[2] on which a 'simple nature' depends.[3] Thus he endeavours[4] to find the form of heat which is a simple
