Having ensured that divine providence played a major role in his mechanical philosophy, Gassendi turned to the question of human freedom in Book III of the “Ethics,” the last part of the Syntagma philosophicum, entitled “On Liberty, Fortune, Fate, and Divination.” In this concluding section of his magnum opus, Gassendi cast his discussion in the form of a debate among the major classical philosophies, particularly Stoicism and Epicureanism. The main issue was freedom – human and divine. While questions about fate, fortune, and divination may, at first glance, appear rather remote from the primary concerns of seventeenth-century natural philosophy, in fact they involve metaphysical issues central to the articulation of the mechanical philosophy: the extent of contingency and necessity in the world, the nature of causality, and the role of providence and the extent of human freedom in a mechanical universe. Gassendi's treatment of these issues reflects his underlying voluntarism.

Since classical times, natural philosophers had dealt extensively with questions about fate, fortune, and divination. The concept of fate was central to Stoicism, which had explained the world as governed by a deterministic, rational ordering principle, the Logos. According to Stoic doctrine, fate is the expression of the Logos in the causal nexus of a deterministic universe.