 In more recent work (e.g., Salmon 1994), prompted in part by a desire to avoid certain counterexamples advanced by Philip Kitcher (1989) to his characterization of mark transmission, Salmon attempted to fashion a theory of causal explanation that completely avoids any appeal to counterfactuals. In this new theory which is influenced by the conserved process theory of causation of Dowe (2000), Salmon defined a causal process as a process that transmits a non-zero amount of a conserved quantity at each moment in its history. Conserved quantities are quantities so characterized in physics—linear momentum, angular momentum, charge, and so on. A causal interaction is an intersection of world lines associated with causal processes involving exchange of a conserved quantity. Finally, a process transmits a conserved quantity from A to B if it possesses that quantity at every stage without any interactions that involve an exchange of that quantity in the half-open interval  \((A,B]\).[8]