 The first things to develop from the conflagration are the elements. Of the four elements, the Stoics identify two as active (fire and air) and two as passive (water and earth). The active elements, or at least the principles of hot and cold, combine to form breath or pneuma.  Pneuma, in turn, is the ‘sustaining cause’ (causa continens, synektikon aition) of all existing bodies and guides the growth and development of animate bodies. What is a sustaining cause? The Stoics think that the universe is a plenum. Like Aristotle, they reject the existence of empty space or void (except that the universe as a whole is surrounded by it). Thus, one might reasonably ask, ‘What marks any one object off from others surrounding it?’ or, ‘What keeps an object from constantly falling apart as it rubs elbows with other things in the crowd?’.  The answer is: pneuma. Pneuma, by its nature, has a simultaneous movement inward and outward which constitutes its inherent ‘tensility.’ (Perhaps this was suggested by the expansion and contraction associated with heat and cold.) Pneuma passes through all (other) bodies; in its outward motion it gives them the qualities that they have, and in its inward motion makes them unified objects (Nemesius, 47J). In this latter respect, pneuma plays something like one of the roles of substantial form in Aristotle for this too makes the thing of which it is the form ‘some this,’ i.e. an individual (Metaph. VII, 17). Because pneuma acts, it must be a body and it appears that the Stoics stressed the fact that its blending with the passive elements is ‘through and through’ (Galen 47H, Alex. Aph. 48C). Perhaps as a result of this, they developed a theory of mixture which allowed for two bodies to be in the same place at the same time. It should be noted, however, that some scholars (e.g. Sorabji, 1988) think that the claim that pneuma is blended through the totality of matter is a conclusion that the Stoics’ critics adversely drew about what some of their statements committed them to. Perhaps instead they proposed merely that pneuma is the matter of a body at a different level of description.