Pneuma () is an ancient Greek word for "breath", and in a religious context for "spirit" or "soul". It has various technical meanings for medical writers and philosophers of classical antiquity, particularly in regard to physiology, and is also used in Greek translations of ruach in the Hebrew Bible, and in the Greek New Testament. In classical philosophy, it is distinguishable from psyche (?), which originally meant "breath of life", but is regularly translated as "spirit" or most often "soul".
Pneuma, "air in motion, breath, wind", is equivalent in the material monism of Anaximenes to aer (, "air") as the element from which all else originated. This usage is the earliest extant occurrence of the term in philosophy. A quotation from Anaximenes observes that "just as our soul (psyche), being air (aer), holds us together, so do breath (pneuma) and air (aer) encompass the whole world." In this early usage, aer and pneuma are synonymous.
In ancient Greek medicine, pneuma is the form of circulating air necessary for the systemic functioning of vital organs. It is the material that sustains consciousness in a body. According to Diocles and Praxagoras, the psychic pneuma mediates between the heart, regarded as the seat of Mind in some physiological theories of ancient medicine, and the brain.
The disciples of Hippocrates explained the maintenance of vital heat to be the function of the breath within the organism. Around 300 BC, Praxagoras discovered the distinction between the arteries and the veins, although close studies of vascular anatomy had been ongoing since at least Diogenes of Apollonia. In the corpse arteries are empty; hence, in the light of these preconceptions they were declared to be vessels for conveying pneuma to the different parts of the body. A generation afterwards, Erasistratus made this the basis of a new theory of diseases and their treatment. The pneuma, inhaled from the outside air, rushes through the arteries till it reaches the various centres, especially the brain and the heart, and there causes thought and organic movement.
The "connate pneuma" of Aristotle is the warm mobile "air" that in the sperm transmits the capacity for locomotion and certain sensations to the offspring. These movements derive from the soul of the parent and are embodied by the pneuma as a material substance in semen. Pneuma is necessary for life, and as in medical theory is involved with the "vital heat," but the Aristotelian pneuma is less precisely and thoroughly defined than that of the Stoics.
In Stoic philosophy, pneuma is the concept of the "breath of life," a mixture of the elements air (in motion) and fire (as warmth). For the Stoics, pneuma is the active, generative principle that organizes both the individual and the cosmos. In its highest form, pneuma constitutes the human soul (psychê), which is a fragment of the pneuma that is the soul of God (Zeus). As a force that structures matter, it exists even in inanimate objects. In his Introduction to the 1964 book Meditations, the Anglican priest Maxwell Staniforth wrote:
Cleanthes, wishing to give more explicit meaning to Zeno's 'creative fire', had been the first to hit upon the term pneuma, or 'spirit', to describe it. Like fire, this intelligent 'spirit' was imagined as a tenuous substance akin to a current of air or breath, but essentially possessing the quality of warmth; it was immanent in the universe as God, and in man as the soul and life-giving principle.
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In Judaic and Christian usage, pneuma is a common word for "spirit" in the Septuagint and the Greek New Testament. At John 3:5, for example, pneuma is the Greek word translated into English as "spirit": "Verily, verily, I say unto thee, Except a man be born of water and of the Spirit (pneuma), he cannot enter into the kingdom of God." In some translations such as the King James version, however, pneuma is then translated as "wind" in verse eight, followed by the rendering "Spirit": "The wind (pneuma) bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit (pneuma)."
Philo, a 1st-century Hellenistic Jewish philosopher commented on the use of ?, rather than , in the Septuagint translation of Genesis 2:7. Philo explains that, in his view, pneuma is for the light breathing of human men while the stronger pno? was used for the divine Spirit.