The change or passage from a negative term to a positive term, from not existing to existing, is called generation (Lat. generatio ); the change or passage from a positive term to a negative term, from existing to not existing, is called destruction or corruption (Lat. corruptio ). Because there is no intermediary between the contradictories "existing" and "not existing," between "affirming" and "denying," generation and corruption are called changes according to contradiction. They are therefore instantaneous. Either one may be "absolute" (simpliciter ) or merely "with respect to something" (secundum quid ). An example of the former is the coming into existence of Socrates, a man, or his ceasing to exist; of the latter, his becoming white or his ceasing to be white, whether he, too, comes to be or ceases to be or not.
Neither generation nor corruption, whether absolute or with respect to something, is motion in the strict sense of the word. Motion requires something already in existence that can be moved gradually from one positive term to another positive term contrary to the first.
In living beings, substantial or absolute generation is a vital operation that proceeds from within the parent as a conjoined principle producing an offspring specifically like itself.
See Also: substantial change; matter and form.