"He who says that all things happen of necessity can hardly find fault with one who denies that all happens by necessity; for on his own theory this very argument is voiced by necessity." That was Epicurus. He and the Epicureans in general believed in an atomistic picture of the world they had picked up from Democritus, but they also believed that atoms sometimes "swerve," that is, change course randomly. I don't know what is the Greek for "swerve" but later Latin authors used the term "clinamen." The French philosopher Gilles Deleuze (above) revived use of "clinamen" as a philosophical term of art inthe late 20th century. But of course, he HAD to do that....