LAW OF CAUSATION. 195 



exception to them; and philosophers have been led, although (as I 

 have endeavored to show) erroneously, to consider their evidence as 

 lying not in experience, but in the original constitution of the human 

 intellect. If, therefore, from the laws of space and number, we were 

 able to deduce unifermitics of any other description, this would be 

 conclusive evidence tu us that those other unifonnities possessed the 

 same degi-ee of rigorous certainty. But this we cannot do. From 

 laws of space and number alone, nothing can be deduced but laws of 

 space and number. 



Of all truths relating to j)henomena, the most valuable to us are 

 those which relate to the order of their succession. On a knowledge 

 of these is founded every reasonable anticipation of future facts, and 

 whatever power we possess of influencing those facts to our advantage. 

 Even the laws of geometry are chiefly of practical importance to us as 

 being a portion of the premisses from which the order of the succession 

 of phenomena may be inferred. 



Inasmuch as the motion of bodies, the action of forces, and the 

 propagation of influences of all sorts, take place in certain lines and 

 over definite spaces, the properties of those lines and spaces are an 

 important part of the laws to which those phenomena are themselves 

 subject. Moreover, motions, forces, or other influences, and times, arc 

 numerable quantities ; and the properties of number are applicable to 

 them as to all other things. But although the laws of number and 

 space are important elements in the ascertainment of uniformities of 

 succession, they can do nothing towards it when taken by themselves. 

 They can only be made instrumental to that purpose when we combine 

 with them additional premisses, expressive of uniformities of succession 

 already known. By taking, for instance, as premisses, these proposi- 

 tions : that bodies acted upon by an instantaneous force move with 

 uniform velocity in straight lines ; tliat bodies acted upon by a con- 

 tinuous force move with accelerated velocity in straight lines ; and 

 that bodies acted upon by two forces in different directions move in 

 the diagonal of a parallelogram, whose sides represent the direction 

 and quantity of those forces ; we may by combining these truths with 

 propositions relating to the properties of straight lines and of parallelo- 

 grams, (as that a tnangle is half of a parallelogram of the same base 

 and altitude,) deduce another important uniformity of succession, viz., 

 that a body moving round a centre of force describes areas propor- 

 tional to the times. But unless there had been laws of succession in 

 our premisses, there could have been no truths of succession in our 

 conclusions. A similar remark might be extended to every other class 

 of phenomena really peculiar ; and, had it been attended to, would 

 have prevented many chimerical attempts at demonstrations of the 

 indemonstrable, and explanations of what cannot be explained. 



It is not, therefore, enough for us that the laws of space, which are 

 only laws of simultaneous phenomena, and the laws of number, which 

 though true of successive phenomena do not relate to their succession, 

 possess that rigorous certainty and universality of which we are in 

 search. "We must endeavor to find some law of succession which has 

 those same attributes, and is therefore fit to be made the foundation of 

 processes for discovering, and of a test for verifying, all other uniformi- 

 ties of succession. This fundamental law must resemble the truths of 

 geometry in their most remarkable peculiarity, that of never being, in 



