  But it is not only processes of generation that conform to this requirement.  Instances of qualitative change are often mentioned alongside substantial generation, and as a crucially important instance of qualitative alteration—or of  qualitative quasi-alteration, depending on how we interpret  Aristotle’s theory of  perception[25]—Aristotle presupposes that the principle of causational synonymy  characterises also the causal link connecting the object of  sensation and the sense organ.   