ABSTRACT
During the early decades of the twentieth century, there was general agreement among scientists and philosophers interested in physics that causal relatedness is a matter of uniformity of sequence and the regularity in question is between states of (relatively isolated) systems. Moritz Schlick pointed out that the starting point of inquiry in physics is the measurement of quantities rather than the description of events. These quantities are values of the state of a physical system. Physicists have found that the horizontal component of the motion of such systems can be predicted if the masses, positions, and velocities of the bodies are specified. Hence, they take mass, position, and velocity to be the state variables of the system and ignore color, chemical composition, and other factors. A causal relation for this system is a functional relationship that describes the spatiotemporal variation of its state. The law of conservation of momentum qualifies as a causal relation.
