 Mulla Sadra is often described as a metaphysical revolutionary because of his uniquely posited doctrine of existence. The analysis of existence commences with the ontological distinction between the Necessary (the principle, God) and the contingent. God is pure existence without essence, quality or property that undergoes change or motion. The origins of this doctrine lie in Avicenna’s account of radical contingency that considers the distinction between Necessary and contingent to be predicated upon the simplicity of existence of the Necessary producing the complexity of the existence and essence of the contingent, where the contingent is an existent to whom accidents pertain bundled in what is known as their ‘essence’. Contingents are conceptually dyads of existence (the fact that they are) and essence (bundles of properties that define what they are, Mulla Sadra 2001–5, I: 289–92). Since God bestows existence upon contingents, or rather because causally contingents derive their existence from their principle, existence is ontologically prior to essence. Analytically, it may seem to us that the reverse is true because our encounter with things and events takes the phenomenal form of acquaintance with the form and essence of that thing first. But in fact, Mulla Sadra’s position on existence is even more radical than the Aristotelian doctrine of pros hen homonymy. Substances are not the primary sense of existence but rather ‘acts of existence’ or processes. In this, and in his doctrine of substantial motion that is discussed below, one can see a systematic rejection of Aristotelian category theory.