FALLACIES OF SIMPLE INSPECTION. 



497 



pole, he might equally prove his point 

 by the principle of the Sufficient Rea- 

 son, By what right is it assumed 

 that a state of rest is the particular 

 state which cannot be deviated from 

 without special cause? Why not a 

 state of motion, and of some parti- 

 cular sort of motion ? Why may we 

 not say that the natural state of a 

 horse left to himself is to amble, be- 

 cause otherwise he must either trot, 

 gallop, or stand still, and because we 

 know no reason why he should do 

 one of these rather than another? 

 If this is to be called an unfair use 

 of the "sufficient reason," and the 

 other a fair one, there must be a 

 tacit assumption that a state of rest 

 is more natural to a horse than a 

 state of ambling. If this means that 

 it is the state which the animal will 

 assume when left to himself, that is 

 the very point to be proved ; and if it 

 does not mean this, it can only mean 

 that a state of rest is the simple.st 

 state, and therefore the most likely 

 to prevail in nature, which is one of 

 the fallacies or natural prejudices we 

 have already examined. 



So again of the First Law of Mo- 

 tion ; that a body once moving will, 

 if left to itself, continue to move uni- 

 formly in a straight line. An attempt 

 is made to prove this law by saying, 

 that if not, the body must deviate 

 either to the right or to the left, and 

 that there is no reason why it should 

 do one more than the other. But 

 who could know, antecedently to ex- 

 perience, whether there was a reason 

 or not ? Might it not be the nature 

 of bodies, or of some particular bodies, 

 to deviate towards the right ? or if 

 the supposition is preferred, towards 

 the east or south ? It was long 

 thought that bodies, terrestrial ones 

 at least, had a natural tendency to 

 deflect downwards ; and there is no 

 shadow of anything objectionable in 

 the supposition, except that it is not 

 true. The pretended proof of the law 

 of motion is even more manifestly 

 untenable than that of the law of 

 inertia, for it is flagrantly inconsis- 



tent ; it assumes that the continu- 

 ance of moti«)n in the direction first 

 taken is more natural than deviation 

 either to the right or to the left, but 

 denies that one of these can possibly 

 be more natural than the other. All 

 these fancies of the possibility of 

 knowing what is natural or not natu- 

 ral by any other means than experi- 

 ence, are, in truth, entirely futile. 

 The real and only proof of the laws 

 of motion, or of any other law of the 

 universe, is experience ; it is simply 

 that no other suppositions explain or 

 are consistent with the facts of uni- 

 versal nature. 



Geometers have, in all ages, been 

 open to the imputation of endeavour- 

 ing to prove the most general facts 

 of the outward world by sophistical 

 reasoning, in order to avoid appeals 

 to the senses. Archimedes, says Pro- 

 fessor Play fair,* establi-shed some of 

 the elementary propositions of statics 

 by a process in which he " borrows no 

 principle from experiment, but estab- 

 lishes his ccmclusion entirely by rea- 

 soning d priori. He assumes, indeed, 

 that equal bodies, at the ends of the 

 equal arms of a lever, will balance 

 one another ; and also that a cylinder 

 or parallelepiped of homogeneous mat- 

 ter will be balanced about its centre 

 of magnitude. These, however, are 

 not inferences from experience ; they 

 are, properly speaking, conclusions 

 deduced from the principle of the 

 Sufficient Reason." And to this day 

 there are few geometers who would 

 not think it far more scientific to 

 establish these or any other premises 

 in this way than to rest their evidence 

 on that familiar experience which in 

 the case in question might have been 

 so safely appealed to. 



§ 6. Another natural prejudice, of 

 most extensive prevalence, and which 

 had a great share in producing the 

 errors fallen into by the ancients in 

 thbir physical inquiries, was this : 

 That the dififerences in nature must 



* Dittertation, ut supra, p. 37. 

 2 I 



