The Principles Beneath Substance

The alchemical principles are the qualities the tradition held to underlie all substance. Chief among them is the tria prima of Paracelsus, sulphur, mercury and salt, standing not for the ordinary materials but for combustibility, volatility and fixity, the three principles into which any substance could be analysed. Behind this lay the older mercury-sulphur theory of the Arabic alchemists, which held all metals to be compounds of a mercurial and a sulphurous principle in varying purity.

These principles are the theoretical core of alchemy's account of matter: the reason metals could, in principle, be transmuted was that they shared the same underlying principles in different proportions and purities.