Note (return) — Chapter XIII

In the system of Epicurus, the soul is regarded as corporeal or material, like the body; they form, together, one nature or substance. The soul is composed of atoms exceedingly diminutive, smooth, and round, and connected with or diffused through the veins, viscera, and nerves. The substance of the soul is not to be regarded as simple and uncompounded; its constituent parts are aura, heat, and air. These are not sufficient, however, even in the judgment of Epicurus, to account for sensation; they are not adequate to generate sensible motives such as revolve any thoughts in the mind. "A certain fourth nature, or substance, must, therefore, necessarily be added to these, that is wholly without a name; it is a substance, however, than which nothing exists more active or more subtile, nor is any thing more essentially composed of small and smooth elementary particles; and it is this substance which first distributes sensible motions through the members." 812