 Thus, in order to define the direction of causation, the conserved quantity accounts need to be supplemented by probabilistic information. It has also been argued that conserved quantity accounts cannot adequately distinguish those features of a process that are explanatorily relevant from those that are not without relying on counterfactuals (Woodward 2003b [2019]). Earman (2014) argues that the most appropriate way to characterize causal processes is in terms of systems governed by equations that allow for a well-posed initial value formulation, which are systems governed by hyperbolic equations (see also Woodward 2016).