"Stoics... thought of the ...[as] an extremely tenuous... physical agency spread continuously throughout the organism... capable of producing physical effects... [T]he pneuma theory... provided... explanation for... the tangible ['passive'] forms of matter (solid and liquid) and the intangible ['active'] ones (fiery and aery)... [T]he different forms of pneuma were composed of varying blends of fire and air. ...When the ethereal pneuma held the... body together in a coherent pattern... it entered into a 'total union'... The psyche and the pneuma became interchangeable terms, which referred equally to a pattern of observable characters and to the hypothetical medium presumed to underlie it."