The transmission of movement

The ultimate source of movement, in Aristotle's system, is the unmoved mover who acts as a final cause, by being loved. The ‘moved movers’—the heavenly bodies or more properly the spheres that carry them—transmit movement in turn as efficient causes. But whereas throughout the heavenly region movement is eternal and unchanging, in the region below the moon there is both movement and change. Change is brought about primarily because the course of the sun in the ecliptic is oblique to the axis of the earth. This oblique course of the sun causes the changes in the seasons, the ceaseless pendulumlike movement between the two extremes of the heat and dryness of summer and the cold and wet of winter, changes which are, of course, a good deal more striking in the Mediterranean than they are in our own more temperate climate.

In making the sun the source of change in the sublunary region Aristotle was no doubt chiefly influenced by the manifest fact that the generation and decay of many living things, especially plants, are closely linked with the seasons. There are, however, several serious difficulties both in his view of the relation between the heavenly and the sublunary regions, and in his theory of the transmission of movement from one to the other, and these must be considered before we discuss his account of the sublunary region as a whole.