vs. vi.] CAUSATION. 155 



inenon. No one pretends tliat we can actually cognize this 

 occulta vis. The deepest analysis of our experience of the act 

 of causation will yield no such element. Viewed under its 

 subjective aspect, our knowledge of causation amounts simply 

 to this, — that an experience of certain invariable sequences 

 among phenomena has wrought in us a set of corresponding 

 indissolubly coherent sequences among our states of con- 

 sciousness ; so that whenever the state of consciousness 

 answering to the cause arises, the state of consciousness 

 answering to the effect inevitably follows. But answering to 

 the occulta vis we have no state of consciousness whatever. 



Moreover the hypothesis of an occulta vis, like so many 

 other metaphysical hypotheses, straightway lands us in an 

 impossibility of thought. The proposition that the cause 

 constrains the effect to follow, is an unthinkable proposition ; 

 since it requires us to conceive the action of matter upon 

 matter, which, as we saw in our first chapter, we can in 

 nowise do. As was there pointed out, neither by the artifice 

 of an intermolecular ether or of centres of attractive and 

 repulsive force, nor by any other imaginable artifice, can we 

 truly conceive one particle of matter acting upon another. 

 What we do know is neither more nor less than what is given 

 in consciousness, namely, that certain coexistences invariably 

 precede or follow certain other coexistences. That matter as 

 objectively existing may exert upon matter some constrain- 

 ing power which, as for ever unknowable by us, may be called 

 an occulta vis, I readily grant. Thought is not the measure 

 of things, and it was therefore unphilosophical in Hume to 

 deny the existence of any such unknown power. Things 

 may exist, in heaven and on earth, which are neither dreamt 

 of in our philosophy nor conceivable by our intelligence. 

 Respecting the external reality we say nothing : we only 

 affirm that no such occulta vis is given in the phenomenon 

 of causation. Any hypothesis which postulates such an 

 unknown element as a means of explaining the phenomenon 



