 As noted above (in section 1.2), Epicurus introduces an indeterministic atomic motion, the swerve, in order to protect human freedom. It is not mentioned in any of the extant texts by Epicurus himself, but a variety of later sources attribute the doctrine to him. The two most extensive discussions we have of the swerve’s role in protecting human freedom are in Cicero’s On Fate, which describes how the swerve is needed in order to preserve the openness of the future and avert the fatalistic implications of the Principle of Bivalence, and in lines 251–293 of Book 2 of On the Nature of Things, Lucretius’ exposition of Epicurean physics.