Its full extension, however, the theory receives in the _De Minimo_, where the atom, or corporeal unity, is not the sole minimum discussed. The full title of the work is:--"On the threefold minimum, and measure, being the principles of the three speculative sciences and of many practical arts." We find nowhere any distinct statement as to what Bruno meant by the "threefold minimum," and the three speculative sciences to which its several members refer. It was supposed that the minima were (1) the monad or unity which is the unit of number, (2) the point, which is the unit of the line, and (3) the atom, which is the unit of body. But arithmetic and geometry can hardly be called speculative sciences, and Tocco has shown that Bruno had in view the triad of _God_, the _soul_ and the _atom_--the three kinds of simple substance, each immortal and indestructible:--_God_ as the supreme and most simple unity, Monad of Monads; _soul_ as that which lives in each composite being and holds in unity the atoms which from time to time enter into its composition; and the _atom_, the most simple of material substances, in the sum of which, with their containing ether, the material universe consists. Had Bruno carried out his subdivision of the speculative sciences, he would probably have referred God, as the substance of all reality, to a speculative theology, of Neoplatonist type; soul as the simple substance of animate beings to metaphysics proper; and the atoms, the substance of body, to a speculative physics, dealing with the metaphysical presuppositions of the general theory of nature, which was set forth in the _De Immenso_. The scheme, however, was never fully carried out,[392] the times being not yet ripe for the complete separation of the speculative and the experimental or observational sciences. In referring the atomic theory to metaphysics, Bruno showed a true instinct, for while in one sense atomism is a scientific hypothesis capable of furnishing laws which explain the interaction of bodies,--the corpuscular theory,--and as such has proved its value by the brilliant developments of recent years, on the other hand, it is also a presupposition of knowledge, a ground of the possibility of our knowledge of body, and therefore has its place in speculative theory, or metaphysics, in the widest sense. Both points of view are presented in Bruno's doctrine, but that from which he starts is the epistemological, following in this the guidance of Nicholas of Cusa. [Sidenote: Knowledge implies the atom.] [Sidenote: Relativity of minimum.]