After their experiments...

After their experiments, scientists remain in need of the principle of causality, for the immediate results of their experiments are nothing but the fact that in the cases tested specific phenomena have occurred simultaneously or following other phenomena. The discovery of a universal law, and the claim that this cause always brings about the appearance of certain effects, requires another principle which can never be obtained by experimentation.

The correct view is that this principle is the very principle of causation, that is, a scientist can present a universal law with certainty only when he has been successful in discovering the common factor in all cases, and he has found the existence of the cause of phenomena in all the cases tested. In this way it may be said that whenever and wherever…