2. Leibnitz next examined the scientific conception of the atom. Gassendi, one of that celebrated group of Parisian scientists, had been the author of the introduction of Greek atomism into modern thought. It had been generally accepted by scientists and combined with the mathematical hypothesis of Galileo. Leibnitz had known Gassendi in Paris, and he took the hard, inelastic atoms of Gassendi under examination. He agreed that the atomist was perfectly correct in saying that material bodies consist of simple parts or atoms. But Leibnitz insisted that the atomist erred in thinking such simple parts to be physical. However simple the parts might physically appear to be, they were not really simple. However small a bit of matter may be, it may be divided again, and the dividing process may go on to infinity. The atom is the extended, and the extended cannot be simple or real. Substance must be unextended, and the materialists were wrong in attributing substance to the extended. Is there anything simple that has a qualitative character? Is there anything real below the physical atoms? Yes, the metaphysical atoms. The indivisible, immaterial unit lies beneath the physical atom, and in order to reach it we must pass beneath the physical into the metaphysical. This immaterial or metaphysical atom is called by Leibnitz the _monad_; and thus is Leibnitz’s theory called _monadology_. There are three kinds of points, or units, or “simples.” There is the mathematical point, which is simple enough, but it is only imaginary. There is the physical point, or atom, which is real but not simple. There is, lastly, the metaphysical point, or monad, which is both real and simple. The metaphysical point is the only true point. To call the material atoms real, only shows “the feebleness of the imagination, which is glad to rest, and is, therefore, in haste to make an end of division and analysis.” 3. Leibnitz then identified force, as the substance of motion, with the metaphysical atom, as the substance of the material atom. The result was the monad, as he conceived it. The monads are the principles of active working. They are the super-spatial and immaterial principles in which the mechanical principles of the universe have their roots and meaning. Nature is not dead; it is not merely extended. It is alive, resistant, and reproductive. If, as Spinoza taught, there were only one substance, nature would be non-resistant and passive. But as a matter of fact there are many substances acting for themselves, many bodies resisting other bodies. They are the centres of separate activity, and there are as many forces as there are things. There is no body without movement, no movement without force. Thus does Leibnitz reintroduce vitalism in a maturer form than is seen in neo-Platonism. Life becomes the principle of nature. Purpose is placed at the centre of things.