COEXISTENCES INDEPENDENT OF CAUSATION. 135 



of species which differ more from one another than 

 either differs from a third, (especially if that third 

 species occupies in most of its known properties a 

 position between the two former,) there is some pro- 

 bability that the same thin^ will also be true of that 

 intermediate species ; for it is often, though by no 

 means universally, found, that there is a sort of paral- 

 lelism in the properties of different kinds, and that 

 their degree of unlikeness in one respect bears some 

 proportion to their unlikeness in others. We see this 

 parallelism in the properties of the different metals; 

 in those of sulphur, phosphorus, and carbon; of 

 oxygen, chlorine, iodine, andbrome; in the natural 

 orders of plants and animals, &c. But there are 

 innumerable anomalies and exceptions to this sort of 

 conformity, or rather the conformity itself is but an 

 anomaly and an exception in nature. 



Universal propositions, therefore, respecting the 

 properties of superior Kinds, unless grounded on 

 proved or presumed connexion by causation, ought 

 not to be hazarded except after separately examining 

 every known sub-kind included in the larger Kind. 

 And even then such generalizations must be held in 

 readiness to be given up on the occurrence of some 

 new anomaly, which, when the uniformity is not 

 derived from causation, can never, even in the case of 

 the most general of these empirical laws, be considered 

 very improbable. Thus all the universal propositions 

 which it has been attempted to lay down respecting 

 simple substances, or concerning any of the classes 

 which have been formed among simple substances 

 (and the attempt has been often made) have, with the 

 progress of experience, either faded into inanity, or 

 been proved to be erroneous; and each Kind of sim- 

 ple substance remains with its own collection of pro- 



