De Anima: from Aristotle to Posidonius
by: M. Horatius Piscinus
The human form seen as composed of body and soul poses a perennial philosophical problem. How can two unlike things be joined together as one' Modern philosophy has tended to resolve the problem by rejecting the idea of a soul as originating exterior to body, Nietzsche's "Body am I entirely, and nothing more; and soul is only the name of something in the body." The soul, or human mind, is seen as a consequence of the formation of the physical body, with attempts to explain thought and emotions solely as physical phenomenon. For those philosophers who recognize a distinction between mind and body, the resolution has been to pose a tertium quid that acts to join both together. With Aristotle this tertium quid is called the pneuma, a spiritual vehicle carrying the soul and linking it to the physical body. Aristotle's pneuma is an outgrowth of the physical body, a part of the physical body that receives the soul, which is common in all life forms, transmitted through procreation. In Nature inanimate bodies may grow through accretion, by the principle of the gnomen, but growth in animate bodies occurs by a geometric progression, doubling in size. Even a simple life form like yeast duplicates itself. Growth in plants and animals results from nutrition, which both seek by employing their powers of sensation and attain through locomotion. As Aristotle would later be elaborated on, his pneuma contains the nutritive or vegetative soul and the sensitive or animal soul. The pneuma as a part of the body, and these lower souls that it contains, perish along with the body.

Later commentators on Aristotle held that his pneuma was "analogous to that element of which the stars are made," i.e. to the pempton soma. In the Timaeus, Plato tells of how the gods "assigned each soul to a star and having placed them there as in a chariot (41e)," and, still referring to the stars, "(the gods) provide the body to be (the soul's) vehicle and means of locomotion (44e)." At Timaeus 69c he says, "(The gods) received from (the God Over All) the immortal principle of the soul; and around this they proceeded to fashion a mortal body, and made it to be the vehicle of the soul, and constructed with the body a soul of another nature which is mortal." Already with Plato, therefore, a tertium quid is suggested, Aristotle's pneuma being Plato's mortal soul. However, Aristotle was speaking only to how a soul is attached to a material body. In other works by Plato there is suggested to be a divine intellect in addition to body and soul. Applying Aristotle's solution of a tertium quid then to the distinction between soul and intellect leads to a multiplication of intermediaries by philosophers of various schools of thought. Part of the stimulus for this multiplication is due to attempts to reconcile the various schools. The Stoic conception of the soul is that of a quasi-material breath of life that is similar to Aristotle's pneuma. The Stoic pneumatic-soul originates among the stars, and upon the dissolution of the body it returns to live in the heavens. The Stoics even come to explain the Milky Way as the souls of the dead travelling between the heavens and earth, which eclectic thinkers will link to Plato's words in the Timaeus.

Posidonius of Apamea (c. 135-50) modified some earlier Stoic thought by referring to Plato. One of his students at Rhodes was Cicero, and later, in 86 BCE, Posidonius visited Cicero in Rome while serving as an ambassador. In Cicero (De Natura Deorum) there is a comment made that all men possess a mind that is "plucked from a divine mind (animus)" following a Platonist notion that human souls originate within Plato's World Soul (anima). Posidonius also equated the Stoic cosmopolis, or human brotherhood, with the Roman Empire as a reflection of the commonwealth of the gods. There is an element of political expediency in Posidonius making such a comparison, but it fitted well to the Roman conception of piety and the role of the religio romana whereby the expansion of the Roman state was dependent upon maintaining an accord with the gods. This is brought out more in Cicero's Dream of Scipio where statesmen and philosophers who prove themselves deserving by performing their duties in accordance with the will of the gods are admitted into the stellar abode of the gods. The earliest mention of Plato's ochema as Aristotle's pneuma is found however with Galen (131- 200 CE). Galen introduced the idea after reviewing Posidonius' theory on sight resulting from an affinity between rays of sunlight with the organ of vision. The idea is that sunrays travel down from the heavens as a Platonic ochema of light and attach to Aristotle's pneuma that holds the sensory soul in the eyes, to make sight possible. There emerged an idea of the soul embodied in a luminous substance with the Platonist Heraclides Ponticus, among some Pythagorans according to Alexander Polyhistor, and among "some of the Aristotlians" according to Iamblichus (d. 330 CE). Later still Proclus expressed this concept as the ochema pneumatikon while commenting on the Timaeus. As with Socrates earlier, responding to popular notions in Orphism, the concept of the soul carried in a body of light enters philosophy, where it is explained in Platonist and Aristotelian terms, in reaction to notions that were prevalent in the religious movements of the second and third centuries.
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