 For all of the philosophers we have treated time and place are relative terms, which respectively depend on a motion and a situated thing for their very existence. In contrast, al-Razi argued that one had to distinguish between the relative conception of these notions and the absolute conception. Thus he distinguished between time (a relative temporal notion) and duration (an absolute temporal notion) as well as between place (a relative spatial notion) and void (an absolute spatial notion). As absolute both duration and void are substances in the sense that they have an existence independent of anything else and thus in principle could exist if everything else failed to exist.