  Even though the foregoing might have suggested that generation of substances is fundamental for all the other kinds of changes, in fact locomotion will have a privileged status.  All other changes depend on locomotions, because any two entities involved in change, with their active and passive potentialities respectively, need to come into contact in order for the interaction to  occur.[32]  Contact, however, as a rule needs to be established by locomotion: either the entity to be moved, or the mover, or both, need to proceed so that they meet (Physics 8.7, 260a26–b7).  Moreover locomotion is the form of change which can occur in isolation of generation, perishing and the other forms of change (Physics 8.7, 260b26–29). Other changes are independent kinds of change insofar as they can occur in an entity which does not perform any other change. Nevertheless all these forms of change include or presuppose that some other entity engages in  locomotion.[33]