APPROXIMATE GENERALIZATIONS. 351 



thiitl, (especially if that third species occupies. in most of its known 

 properties a position between the two former,) there is some proba- 

 bility that the same thing will also be true of that intermediate fepecies; 

 for it is often, though by no means universally, found, that there is a 

 sort of parallelism in the properties of diflbrent 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, and brome ; in the natural ordws of plants 

 and animals, &c. But there are innumerable anomalies and excep- 

 tions to this sort of conformity, or rather the.conformitv itself is but an 

 anomaly and an exception in nature. 



Universal propositions, therefore, respecting the properties of su- 

 perior Kinds, unless grounded on proved or presumed connexion by 

 causation, ought not to be hazarded except after separately examining 

 evej-y 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 emjjirical 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 simple 

 substance remains with its own collection of properties apart from the 

 rest, saving a certain parallelism with a few other Kinds, the most 

 similar to itself. In organized beings, indeed, there are abundance of 

 propositions ascertained to be universally true of superior .genera, to 

 many of which the discovery hereafter of any exceptions must be 

 regarded as supremely improbable. But these, as already observed, 

 are, we have every reason to believe, truths dependent upon causation. 



Uniformities of coexistence, then, not only when they are conse- 

 quences .of laws of succession, but also when they are ultimate truths, 

 must be ranked, for the purposes of logic, among empirical laws ; and 

 are amenable in every respect to the same rules with those unresolved 

 uniformities which are known to be dependent upon causation. 



CHAPTER XXIII. 



OF APPROXIMATE GENERALIZATIONS, AND PROBABLE EVIDENCE. 



§ 1. In our inquiries into the nature of the inductive process, we 

 have hitherto confined our notic(? to such generalizations from experi- 

 ence as profess, to be universally true, We indeed recognized a 

 distinction between generalizations which are certain and those which 

 are only probable : but tho propositions themselves, though they 

 differed in being more or less doubtful in tho one case, and not at all 

 doubtful in the other, were always of the form. Every A is B ; they 

 claimed nothing less than universality, whatever might be the com- 



