CAUSATION 



would cease to take place. The series of the 

 earth's motions, therefore, though a case of 

 sequence invariable within the limits of human 

 experience, is not a case of causation. It is not 

 unconditional."^ July does not cause August, 

 though it invariably precedes it. For the se- 

 quence is conditioned by the coexistence of a 

 given ratio between the solar gravitation and 

 the earth's tangential momentum, with a given 

 inclination of the earth's axis of rotation to the 

 plane of its orbit. Vary either of these factors, 

 which are the real causes of the seasons, and 

 the hitherto invariable sequence between July 

 and August will be altered. 



Causation may therefore be defined as the 

 unconditional invariable sequence of one event, 

 or concurrence of events, upon another ; and 

 this is all that is given in the phenomenon. But 

 metaphysics is not content with this conception 

 of Cause. It prefers to regard causation as a 

 kind of constraint by which the antecedent event 

 obliges the consequent event to follow it. It 

 postulates a hidden power, an occulta vis^ in the 

 cause, which operates as an invincible nexus 

 between it and the effect. And it is by virtue 

 of the exertion of this occult energy that cause, 

 as formulated by metaphysics, is called Efficient 

 Cause, in distinction from the only, cause known 

 to science, — the unconditional invariable an- 



^ Mill, System of Logic, 6th edition, vol.j. pp. 379-381. 

 227 



