Love and Strife
The four elements are, however, simple, eternal, and unalterable, and as change is the consequence of their mixture and separation, it was also necessary to suppose the existence of moving powers - to bring about mixture and separation. The four elements are eternally brought into union, and eternally parted from each other, by two divine powers, Love and Strife. Love (Greek: φιλία) explains the attraction of different forms of matter, and Strife (Greek: νεῖκος) accounts for their separation.[31] If the elements are the content of the universe, then Love and Strife explain their variation and harmony. Love and Strife are attractive and repulsive forces which the ordinary eye can see working amongst people, but which really pervade the universe. They alternately hold empire over things, - neither, however, being ever quite absent.
http://en.wikipedia.org/wiki/Empedocles#cite_note-29