Proposition VI.

The existence of an infinite number of causes and effects is impossible, even if these were not magnitudes; if, e.g., one Intelligence were the cause of a second, the second the cause of a third, the third the cause of a fourth, and so on, the series could not be continued ad infinitum.

Four categories are subject to change:—

(a.) Substance.—Changes which affect the substance of a thing are called genesis and destruction.

(b.) Quantity.—Changes in reference to quantity are increase and decrease.

(c.) Quality.—Changes in the qualities of things are transformations.

(d.) Place.—Change of place is called motion.

The term “motion” is properly applied to change of place, but is also used in a general sense of all kinds of changes.

The motion of a thing is either essential or accidental; or it is due to an external force, or to the participation of the thing in the motion of another thing. This latter kind of motion is similar to the accidental one. An instance of essential motion may be found in the translation of a thing from one place to another. The accident of a thing, as, e.g., its black colour, is said to move when the thing itself changes its place. The upward motion of a stone, owing to a force applied to it in that direction, is an instance of a motion due to an external force. The motion of a nail in a boat may serve to illustrate motion due to the participation of a thing in the motion of another thing; for when the boat moves, the nail is said to move likewise. The same is the case with everything composed of several parts: when the thing itself moves, every part of it is likewise said to move.