62. The Stoic System of Physics. -- The Stoic physics may be summed up in four principal theses: Materialism, Dynamism, Pantheism, and Determinism.

(1) Materialism. -- Corporeal things are the only real things. By the word body (Corpus) we must understand not only corporeal substances, but also their properties, -- even the knowledge, feelings, and virtues which affect these substances. However, the Stoics elsewhere relax the rigour of this very extreme teaching, and, despite the contradiction involved, admit that certain incorporeal things exist, amongst which is the lekton or the object of our universal ideas (63). Since the properties of things can be reduced to matter, and are nevertheless distinct from the substance in which they appear, the Stoics admit the compenetration of material particles in the same place. This is the krasis di holôn.^{1}

(2) Dynamism (7). -- The principle of the internal force which energizes matter is warm air (pneuma), often identified with heat or fire. The different degrees of tension (tonos) of this pneuma explain the various properties and states of bodies (Heraclitus).

(3) Pantheism. -- The pneuma is one. If we make an exhaustive analysis of the various forms of activity, we find that they all spring from one supreme and perfect cause whose unity of action can alone explain the beauty, harmony, and finality of the world. God is air, heat, fire; He is also intelligence, goodness, world-soul. Thus, combining physical and intellectual attributes, we might say that God is the intelligent-fire-soul of the world. And as force (pneuma) is an internal principle of matter (2), and is itself material (1), God is both the primal matter and the dynamic principle of all things. The things of nature are but overflowings of the Divine matter, breathings of the Divine spirit.

To signify this plastic force of the supreme pneuma the Stoics have called it the logos spermatikos, the generating idea, just as they have applied the title logoi spermatikoi, seminal reasons or principles, to the various natural forces in bodies, and especially to that which is inherent in the human soul.

(4) Cosmic Determinism follows as a corollary from dynamic pantheism. The world is a closed system of connected phenomena, each of which is representative of a certain stage of the Divine evolution. The Deity evolves itself naturally and of absolute necessity; and this absolute necessity of every phase of Divine evolution is called fate (heimarmenê). The foreknowledge of God extends to all this, but He has to undergo it. The Stoics attempted in vain to reconcile the existence of physical and moral evil with this theory.

{1} The Stoics worked Out a very remarkable philosophical terminology.