  Stoic physics allows for three different kinds of pneuma (lit. ‘breath’), a breath-like material compound of two of the four Stoic elements, fire and air. The kinds of pneuma differ both in degree of tension that results from the expanding and contracting effects, respectively, of its two constituents, and in their consequent functionality. The lowest kind accounts for the cohesion and character of inanimate bodies (e.g., rocks); the intermediate kind, called natural pneuma, accounts for the vital functions characteristic of plant life; and the third kind is soul, which accounts for the reception and use of impressions (or representations) (phantasiai) and impulse (hormê: that which generates animal movement) or, to use alternative terminology, cognition and desire. Our evidence, which unfortunately is fragmentary and often unclear, suggests strongly that according to the Stoic theory, the body of an animal (human or non-human) contains pneuma of all the three kinds, with the lowest kind responsible for the cohesion and character of parts like teeth and bones, natural pneuma in charge of metabolism, growth and the like, and finally soul accounting for distinctively mental or psychological functions, crucially cognition, by sense and (in the case of humans) intellect, and desire (cf. Long 1999, 564, for discussion and references). If this is indeed the picture that the theory presents, the soul is no longer responsible for all vital functions, and for all aspects of life, but only for specifically mental or psychological functions. (Accordingly, the Stoics depart from the Platonic and Aristotelian view that plants are ensouled organisms.) At the same time, the Stoic theory does attempt to explain non-mental vital functions as well, in terms of the activity of ‘nature’, the intermediate kind of pneuma.  In severing the deeply entrenched, Greek ordinary-language connection between soul and life in all its forms, the Stoic theory is taking an enormously momentous step, one that obviously restricts rather dramatically the proper subject matter of a theory of soul. In fact it is arguable that the Stoics, in limiting the functions of soul in the way they did, played an important role in a complicated history that resulted in the Cartesian conception of mind, according to which the mind plainly is not something that animates living bodies. This narrowing of the conception of soul is one of two aspects of the Stoic theory that, for our purposes, deserve particular notice. 