The Creation of the World Soul
Timaeus then explains how the soul of the world was created (Plato's following discussion is obscure, and almost certainly intended to be read in light of the Sophist). The demiurge combined three elements: two varieties of Sameness (one indivisible and another divisible), two varieties of Difference (again, one indivisible and another divisible), and two types of Being (or Existence, once more, one indivisible and another divisible). From this emerged three compound substances, intermediate (or mixed) Being, intermediate Sameness, and intermediate Difference. From this compound one final substance resulted, the World Soul. He then divided following precise mathematical proportions, cutting the compound lengthways, fixed the resulting two bands in their middle, like in the letter Χ (chi), and connected them at their ends, to have two crossing circles. The demiurge imparted on them a circular movement on their axis: the outer circle was assigned Sameness and turned horizontally to the right, while the inner circle was assigned to Difference and turned diagonally and to the left (34c-36c).
The demiurge gave the primacy to the motion of Sameness and left it undivided; but he divided the motion of Difference in six parts, to have seven unequal circles. He prescribed these circles to move in opposite directions, three of them with equal speeds, the others with unequal speeds, but always in proportion. These circles are the orbits of the heavenly bodies: the three moving at equal speeds are the Sun, Venus and Mercury, while the four moving at unequal speeds are the Moon, Mars, Jupiter and Saturn (36c-d). The complicated pattern of these movements is bound to be repeated again after a period called a 'complete' or 'perfect' year (39d).
Then, the demiurge connected the body and the soul of the universe: he diffused the soul from the center of the body to its extremities in every direction, allowing the invisible soul to envelop the visible body. The soul began to rotate and this was the beginning of its eternal and rational life (36e).
Therefore, having been composed by Sameness, Difference and Existence (their mean), and formed in right proportions, the soul declares the sameness or difference of every object it meets: when it is a sensible object, the inner circle of the Diverse transmit its movement to the soul, where opinions arise, but when it is an intellectual object, the circle of the Same turns perfectly round and true knowledge arises (37a-c).