308 Modality. [CHAP. XIIL 



the outer sidereal sphere down to the lunar sphere, celestial 

 substance was a necessary existence and energy, sempiternal 

 and uniform in its rotations and influence ; and that through 

 its beneficent influence, pervading the concavity between the 

 lunar sphere and the terrestrial centre (which included the 

 four elements with their compounds) there prevailed a regu 

 larizing tendency called Nature; modified, however, and 

 partly counteracted by independent and irregular forces called 

 Spontaneity and Chance, essentially unknowable and unpre 

 dictable. The irregular sequences thus named by Aristotle 

 were the objective correlate of the Problematical Proposition 

 in Logic. In these sublunary sequences, as to future time, 

 may or may not, was all that could be attained, even by the 

 highest knowledge ; certainty, either of affirmation or nega 

 tion, was out of the question. On the other hand, the neces 

 sary and uniform energies of the celestial substance, formed 

 the objective correlate of the Necessary Proposition in Logic ; 

 this substance was not merely an existence, but an existence 

 necessary and unchangeable... he considers the Problematical 

 Proposition in Logic to be not purely subjective, as an 

 expression of the speaker s ignorance, but something more, 

 namely, to correlate with an objective essentially unknowable 

 to all.&quot; 



14. Even after this philosophy began to pass away r 

 the divisions of modality originally founded upon it might 

 have proved, as De Morgan has remarked 1 , of considerable 

 service in mediseval times. As he says, people were much 

 more frequently required to decide in one way or the other 

 upon a single testimony, without there being a sufficiency of 

 specific knowledge to test the statements made. The old 

 logician &quot; did not know but that any day of the week might 

 bring from Cathay or Tartary an account of men who ran on 

 1 Formal Logic, p. 233. 



