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60 occurred to him early in life, and the conviction that all change consists of motion, and that sense-qualities are purely subjective, probably occurred about the same time (ca. 1630), at any rate before his acquaintance with Galileo and Gassendi.

At the outbreak of the revolution Hobbes left England and spent a number of years in France, where for a time he was tutor to the fugitive king Charles II. He returned under Cromwell, devoting himself privately to literary pursuits, occupied with studies and polemics until his death at the venerable age of ninety-one years. The series of articles and the splendid volume in Fromann’s Philosopische Klassiker by Ferdinand Tönnies have contributed much towards a clear understanding of Hobbes’ development and his philosophical significance.

Hobbes’ chief works are: Elements of Law (1640), De cive (1642), Leviathan (1651), De corpore (1655), De homine (1658).

a. Hobbes’ first concern in the systematic presentation of his theory given in the De corpore is to establish the fundamental principles of investigation. He is certain that these principles must be discovered by a process of analytical regression from the given to that which explains it (a sensum ad inventionem principiorum), just as he had previously in fact arrived at the doctrine of motion by a similar regression from sensation. But, on the other hand, he strongly emphasized the fact that the assumption of principles is purely an arbitrary matter, and must necessarily consist of a choice. He does not therefore regard such an analysis as a demonstration; deduction is the only method of demonstration, and this is impossible in the case of first principles.—Hobbes described the arbitrary act with which science begins more precisely as an