 This principle enabled Lavoisier to put what was essentially Aristotle’s notion of simple substances (302a15ff., quoted in section 1.1) to much more effective experimental use. Directly after rejecting atomic theories, he says “if we apply the term elements, or principles of bodies, to express our idea of the last point which analysis is capable of reaching, we must admit, as elements, all the substances into which we are capable, by any means, to reduce bodies by decomposition” (1789, p. xxiv). In other words, elements are identified as the smallest components of substances that we can produce experimentally. The principle of the conservation of mass provided for a criterion of when a chemical change was a decomposition into simpler substances, which was decisive in disposing of the phlogiston theory. The increase in weight on calcination meant, in the light of this principle, that calcination was not a decomposition, as the phlogiston theorists would have it, but the formation of a more complex compound.