Full Idea
What fresh cause exists in nature to make the atom swerve (or do the atoms cast lots among them which is to swerve and which not?), or to serve as the reason for making a very small swerve and not a large one, or one swerve, and not two or three swerves?
Gist of Idea
What causes atomic swerves? Do they draw lots? What decides the size or number of swerves?
Source
comment on Epicurus (fragments/reports [c.289 BCE]) by M. Tullius Cicero - On Fate ('De fato') 20.46
Book Reference
Cicero: 'On Fate, Stoic Paradoxes, Oratory', ed/tr. Rackham,H. [Harvard Loeb 1942], p.243
A Reaction
This is an appeal to the Principle of Sufficient Reason, which seems to be the main ground for rejecting the swerve. The only reason to accept the swerve is reluctance to accept determinism or fatalism.