  Versions of atomism developed by seventeenth-century mechanical philosophers, referred to hereafter as mechanical atomism, were revivals of Ancient Greek atomism, with the important difference that they were presumed to apply only to the material world, and not to the spiritual world of the mind, the soul, angels and so on. Mechanical atomism was a totally general theory, insofar as it offered an account of the material world in general as made up of nothing other than atoms in the void. The atoms themselves were characterised in terms of just a few basic properties, their shape, size and motion. Atoms were changeless and ultimate, in the sense that they could not be broken down into anything smaller and had no inner structure on which their properties depended. The case made for mechanical atomism was largely prior to and independent of empirical investigation.