408 INDUCTION. 



nomena invariably co-existent; and their co-existence can equally be de- 

 duced from the laws of their production. 



It is an obvious question, therefore, whether all the uniformities of co-ex- 

 istence among phenomena may not be accounted for in this manner. And 

 it can not be doubted that between phenomena which are themselves ef- 

 fects, the co-existences must necessarily depend on the causes of those phe- 

 nomena. If they are effects immediately or remotely of the same cause, 

 they can not co-exist except by virtue of some laws or properties of that 

 cause ; if they are effects of different causes, they can not co-exist unless it 

 be because their causes co-exist ; and the uniformity of co-existence, if such 

 there be, between the effects, proves that those particular causes, within the 

 limits of our observation, have uniformly been co-existent. 



§ 2. But these same considerations compel us to recognize that there 

 must be one class of co-existences which can not depend on causation : the 

 co-existences between tlie ultimate properties of things — those j^roperties 

 which are the causes of all phenomena, but are not themselves caused by 

 any phenomenon, and a cause for which could only be sought by ascending 

 to the origin of all things. Yet among these ultimate properties there are 

 not only co-existences, but uniformities of co-existence. General proposi- 

 tions may be, and are, formed, which assert that whenever certain proper- 

 ties are found, certain others are found along with them. We perceive an 

 object ; say, for instance, water. We recognize it to be water, of course by 

 certain of its properties. Having recognized it, we are able to affirm of it 

 innumerable other properties ; which we could not do unless it were a gen- 

 eral truth, a law or uniformity in nature, that the set of properties by 

 which we identify the substance as water always have those other proper- 

 ties conjoined with them. 



In a former place* it has been explained, in some detail, what is meant 

 by the Kinds of objects ; those classes which differ from one another not 

 by a limited and definite, but by an indefinite and unknown, number of dis- 

 tinctions. To this we have now to add, that every proposition by which 

 any thing is asserted of a Kind, affirms a uniformity of co- existence. 

 Since we know nothing of Kinds but their properties, the Kind, to us, is 

 the set of properties by which it is identified, and which must of course be 

 sufficient to distinguish it from every other kind.f In affirming any thing, 

 therefore, of a Kind, we are affirming something to be uniformly co-exist- 

 ent with the properties by which the kind is recognized; and that is the 

 sole meaning of the assertion. 



Among the uniformities of co-existence which exist in nature, may hence 

 be numbered all the properties of Kinds. The whole of these, however, 

 are not independent of causation, but only a portion of them. Some are 

 ultimate properties, others derivative : of some, no cause can be assigned, 

 but others are manifestly dependent on causes. Thus, pure oxygen gas is 

 a Kind, and one of its most unequivocal properties is its gaseous form ; 



* Book i., chap. vii. 



t In some cases, a Kind is sufficiently identified by some one remarkable property : but 

 most commonly several are required ; each property considered singly, being a joint property 

 of that and of other Kinds. The color and brightness of the diamond are common to it with 

 the paste from which false diamonds are made ; its octohedral form is common to it with 

 alum, and magnetic iron ore; but the color and brightness and the form together, identify its 

 Kind ; that is, are a mark to us that it is combustible ; that when burned it produces carbon- 

 ic acid ; that it can not be cut with any known substance ; together with many other ascer- 

 tained properties, and the fact that there exist an indefinite number still unascertained. 



