Jowett: kinds of soul

The bones and flesh, and other similar parts of us, were made as follows. The first principle of all of them was the generation of the marrow. For the bonds of life which unite the soul with the body are made fast there, and they are the root and foundation of the human race. The marrow itself is created out of other materials : God took such of the primary triangles as were straight and smooth, and were adapted by their perfection to produce fire and water, and air and earth — these, I say, he separated from their kinds, and mingling them in due proportions with one another, made the marrow out of them to be a universal seed of the whole race of mankind ; and in this seed he then planted and enclosed the souls, and in the original distribution gave to the marrow as many and various forms as the different kinds of souls were hereafter to receive. That which, like a field, was to receive the divine seed, he made round every way, and called that portion of the marrow, brain, intending that, when an animal was perfected, the vessel containing this substance should be the head ; but that which was intended to contain the remaining and mortal part of the soul he distributed into figures at once around and elongated, and he called them all by the name "marrow" ; and to these, as to anchors, fastening the bonds of the whole soul, he proceeded to fashion around them the entire framework of our body, constructing for the marrow, first of all a complete covering of bone. TIMAEUS  

I have often remarked that there are three kinds of soul located within us, having each of them motions, and I must now repeat in the fewest words possible, that one part, if remaining inactive and ceasing from its natural motion, must necessarily become very weak, but that which is trained and exercised, very strong. Wherefore we should take care that the movements of the different parts of the soul should be in due proportion. TIMAEUS