Sometimes...

Sometimes, numerous motions are directly attributed to a moving object, but sometimes, motion occurs in a moving object by means of another motion, without which it could not occur, as in the serpentine motion of the earth which is obtained by means of its revolutions, which is in fact an attribute of this motion, or the motion of an automobile which is attributed to the gradual increase or decrease of its speed (acceleration), or the substantial motion of bodies, which are attributed with intensity and perfection.

These sorts of motions are called motions superimposed on motions . As was previously said, the concept of speed is obtained through the relation between time and distance. Hence, speed is not attributed to time itself, and naturally, acceleration or the increase and decrease in speed will also have no meaning for time.

Therefore, when it is said that time has passed quickly or slowly, this is called ‘psychological time’ and is a loose way of speaking, and it depends on the quality of the perception of the passage of time. Such ideas may also be applied to physical time.

Types of Substantial Motion Substantial motion, like other kinds of motion does not by itself necessitate perfection and intensity, and the arguments for its existence do not prove anything more than gradual change and renewal of the existence of a substance.

Therefore, as in the case of accidental motion, three states may be posited for it, or it may be divided into three types: Constant motion in which all the potential parts of the substance are equal with respect to perfection and level of existence. Intensifying motion in which every assumed part is more perfect than the previous part. Weakening or declining motion in which every part is weaker and more defective than its predecessor.

Intensifying and weakening motions can be considered to be composed of two motions: (1) one which occurs to the moving thing by means of another; (2) motion without an intermediary, which represents the persistence of a substance, whereas the mediated motion represents its perfection or decline. It is like accelerating motion, whose increase or decrease in speed is considered an ascending or declining motion over spatial or another kind of motion.

A motion that begins with positive acceleration and then has negative acceleration can be represented in the form of a straight line over which from the beginning a curve rises and then falls back to meet the straight line at its end point.