  The link between events and times has, however, been explored also in the opposite direction. If events are assumed as a primitive ontological category, then one may dispense with temporal instants or intervals and construe them as derived entities. The most classical treatment of this sort proceeds by construing temporal instants as maximal sets of pairwise simultaneous (or partially simultaneous) events (Russell 1914; Whitehead 1929; Walker 1947), but other treatments are possible. For example, it has been suggested that the mathematical connection between the way events are perceived to be ordered and the underlying temporal dimension is essentially that of a free construction (in the category-theoretic sense) of linear orderings from event orderings, induced by the binary relation x wholly precedes y (Thomason 1989). Treatments such as these provide a reduction of time in terms of relations among events and are therefore especially germane to a relational conception of time (and, more generally, of space-time). Modal variants (Forbes 1993) as well as mereological variants (Pianesi &amp; Varzi 1996) of such views are also available.