152 DISCOURSE ON THE STUDY 



the increased or diminished intensity of the 

 cause, in cases which admit of increase and di- 

 minution. 



4-th, Proportionality of the effect to its cause in 

 all cases of direct unimpeded action. 



5th, Reversal of the effect with that of the cause. 



(146.) From these characters we are led to the 

 following observations, which may be considered as 

 so many propositions readily applicable to particular 

 cases, or rules of philosophizing: we conclude, 

 1st, That if in our group of facts there be one in 

 which any assigned peculiarity, or attendant cir- 

 cumstance, is wanting or opposite, such peculiarity 

 cannot be the cause we seek. 



(14-7.) 2d, That any circumstance in which all 

 the facts without exception agree, may be the 

 cause in question, or, if not, at least a collateral 

 effect of the same cause: if there be but one 

 such point of agreement, this possibility becomes a 

 certainty ; and, on the other hand, if there be more 

 than one, they may be concurrent causes. 



(148.) 3d, That we are not to deny the existence 

 of a cause in favour of which we have a unanimous 

 agreement of strong analogies, though it may not be 

 apparent how such a cause can produce the effect, 

 or even though it may be difficult to conceive its 

 existence under the circumstances of the case ; in 

 such cases we should rather appeal to experience 

 when possible, than decide a priori against the cause, 

 and try whether it cannot be made apparent. 



(149.) For instance : seeing the sun vividly lumi- 

 nous, every analogy leads us to conclude it intensely 

 hot. How heat can produce light, we know not ; 



