Note 30 — CHAP. III.

Galileo exposes unsparingly the Aristotelian style of reasoning. The reader may take the following from him as a specimen of its quality. The object is to prove the immutability and incorruptibility of the heavens; and thus it is done:—

I. Mutation is either generation or corruption.

II. Generation and corruption only happen between contraries.

III. The motions of contraries are contrary.

IV. The celestial motions are circular.

V. Circular motions have no contraries.

α. Because there can be but three simple motions.

1. To a centre. 2. Round a centre. 3. From a centre.

β. Of three things, one only can be contrary to one.

γ. But a motion to a centre is manifestly the contrary to a motion from a centre.

δ. Therefore a motion round a centre (i. e. a circular motion) remains without a contrary.

VI. Therefore celestial motions have no contraries—therefore among celestial things there are no contraries—therefore the heavens are eternal, immutable, incorruptible, and so forth.

It is evident that all this string of nonsense depends on the excessive vagueness of the notions of generation, corruption, contrariety, &c. on which the changes are rung.—See Galileo, Systema Cosmicum, Dial. i. p. 30.