126 THE SCIENCE OF LOGIC 



those changes or activities suggests or reveals to us, at least 

 partially, the nature of their causes and of the laws according to 

 which these causes interact for &quot; operari sequitur esse&quot; and 

 inasmuch as hypotheses of law thus inevitably suggest hypotheses 

 of cause, the former as well as the latter have some claim to be 

 called hypotheses in the stricter sense, i.e. explanatory hypotheses. 



Some hypotheses, whether they appear descriptive or ex 

 planatory, may be recognized from the beginning as having little 

 or no probability. We may know so little about some unfamiliar, 

 unexplored, complex, many-sided phenomena such as those of 

 electricity, for example as to be scarcely able to make any sup 

 position at all as to their real nature, laws, and causes. But 

 some provisional supposition as to the nature of the agent we call 

 electricity, is absolutely necessary if we want to collect, arrange, 

 describe, and discuss, in intelligible language, its various manifesta 

 tions, and their connexion with their supposed common cause. 

 And this supposition, moreover, if it is to be of any use in help 

 ing us towards an explanation of the phenomena, must be based 

 on some analogy with some known agent. If we make any sup 

 position at all, from which we can infer anything, about the un 

 known thing we call &quot;electricity,&quot; we must suppose the latter to 

 be something resembling in some way or other some known natural 

 agent. Accordingly, the supposition was made by Franklin, 

 if only as a starting-point for investigation, and to see how it 

 would work in other words, as a working hypothesis, that 

 electricity was a fluid of some sort. This hypothesis, though 

 scarcely probable, and merely &quot; better than none,&quot; the best per 

 haps in the circumstances, purported from the beginning to be 

 mainly descriptive, but was none the less, of its nature, explanatory 

 also, inasmuch as it supposed the real cause of the phenomena in 

 question to be some sort of fluid. That hypothesis was never 

 verified, and gradually lost ground, at least in its original form ; 

 though the &quot; electron &quot; hypothesis, which is closely analogous to 

 it, is now in turn taking the place of the two-fluid hypothesis. 



In other cases, however, such working hypotheses may for a 

 long period grow steadily in probability according as they are 

 found capable of explaining a larger area of phenomena, as did the 

 Ptolemaic or geocentric hypotheses (in astronomy), with their 

 cycloids and epicycloids to account for the apparent motions of 

 the planets. 1 So admirably did this group of hypotheses &quot; ex- 

 1 Cf. JOSEPH, op. cit., p. 435. 



