Stoic physics

Stoic physics is the natural philosophy adopted by the Stoic philosophers of ancient Greece and Rome used to explain the natural processes at work in the universe. To the Stoics the universe is a single pantheistic God, but one which is also a material substance. The primitive substance of the universe is a divine essence (pneuma) which is the basis of everything which exists. The separation of force from matter produces a divine fire (aether) which, as the basis of all matter, is differentiated into elements and shaped by the tension caused by the pneuma working according to the divine reason (logos) of the universe. These processes are responsible for the formation, the development, and ultimately, the destruction of the universe in a never-ending cycle (palingenesis). The human soul is an emanation from the fiery aether which permeates the universe, and sensation is transmission of pneuma-currents from objects, which interact with the substance of the mind, which is the soul's ruling part. The Stoics also recognised the existence of other gods and divine agents as manifestations of the one primitive God-substance.

Stoic physics can be described in terms of (a) materialism, (b) dynamic materialism, and (c) monism or pantheism.

Philosophers since the time of Plato had asked whether abstract qualities of the soul, such as justice and wisdom, have an independent existence. In particular, could something that was not visible and tangible be said to exist. The Stoics' answer to this dilemma was to assert that everything, including wisdom, justice, etc., are corporeal. Plato had defined being as "that which has the power to act or be acted upon," and for the Stoics this meant that all action proceeds by bodily contact; every form of causation is reduced to the efficient cause, which implies the communication of motion from one body to another. Only Body exists. Stoicism was thus fully materialistic; the answers to metaphysics are to be sought in physics; particularly the problem of the causes of things for which the Platonic Theory of Forms and the Peripatetic "constitutive form" had been put forth as solutions.

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