The primary stimulus for the ongoing nature of the debate is a paper by David Malament (1977), in which he argues that standard simultaneity is the only simultaneity relation that can be defined, relative to a given inertial frame, from the relation of (symmetric) causal connectibility. Although some commentators have taken Malament’s argument to have settled the debate, others have taken issue with various aspects of his argument. For example, Sahotra Sarkar and John Stachel (1999, pp. 214–215) argue that Malament’s requirement that a simultaneity relation be invariant under temporal reflections is unwarranted, and Grunbaum (2001, pp. 4–5) argues that Malament’s requirement that a simultaneity relation be an equivalence relation is a nontrivial convention. Grunbaum (2001) also endorses and expands upon an earlier argument (Janis,
1983b) that ruling out the introduction of an inertial observer who is not at rest in the given frame, which introduction allows a Malament-like argument for a nonstandard simultaneity relation, is tantamount to requiring at the outset that the one-way speed of light be isotropic.