Richard M. Adler

An event a nonsimultaneous with another event b belongs either to b's past or future. The ground for assigning events to one or the other of these two classes is known as temporal directionality. This dissertation examines three analyses of D, formulated within the contexts of general theories of spacetime. ;The substantivalist represents D as a nonphysical vector field, anchored by a nonmaterial spacetime : a belongs to b's past just in case the spacetime individuals occupied by b and a are connected by a "past-pointing" vector in D. A variant of Leibniz's Identity of Indiscernibles argument is presented, which demonstrates that S gives rise to formally distinct, but empirically indistinguishable, world models. S's model theoretical redundancy undermines the substantivalist's analysis of temporal directionality in that S supports the time-ordering field D. More aggressive Leibnizian attacks on substantival temporal directionality are proven to be unsuccessful. ;The reductionist defines D, using temporally asymmetrical, physical relations. Typically, "past-pointing" is reconstructed via the direction of decreasing entropy gradients in thermodynamical systems. The reductionist's underlying interpretation of entropy is proven to be both scientifically unsupportable and philosophically problematic. Furthermore, it is shown that causal reductionism, the "parent" spacetime program for the entropic account, is scientifically inferior to substantivalism, and that the use of possibilia in constructing causal "physical" world models incurs the Leibnizian empiricist objection again. ;The algebraic absolutist asserts that our world instantiates an abstract, algebraic structure, the nature of which is reflected in the causal behavior of material bodies and events. It is argued that the Leibnizian objection is circumvented by this synthesis: nonphysical spacetime structures are dissociated, or mathematically extracted, from the substantivalist posit S. The exemplification of these structures in our world is epistemically accessible via inferences based on the world's causal structure, under a nonreductionist interpretation. D is now interpreted as the abstract algebraic structure underlying the substantivalist's time-ordering field. The instantiation of this structure by our world is revealed empirically through the unidirectionality of cause-effect relationships among events.