CHAPTER XIII. 



ON THE CONCEPTION AND TREATMENT OF MODALITY. 



1. THE reader who knows anything of the scholastic 

 Logic will have perceived before now that we have been 

 touching in a variety of places upon that most thorny and 

 repulsive of districts in the logical territory ; modality. It 

 will be advisable, however, to put together, somewhat more 

 definitely, what has to be said upon the subject. I propose, 

 therefore, to devote this chapter to a brief account of the 

 principal varieties of treatment which the modals have re 

 ceived at the hands of professed logicians. 



It must be remarked at the outset that the sense in 

 which modality and modal propositions have been at various 

 times understood, is by no means fixed and invariably the 

 same. This diversity of view has arisen partly from cor 

 responding differences in the view taken of the province and 

 nature of logic, and partly from differences in the philo 

 sophical and scientific opinions entertained as to the con 

 stitution and order of nature. In later times, moreover, 

 another very powerful agent in bringing about a change in 

 the treatment of the subject must be recognized in the 

 gradual and steady growth of the theory of Probability, as 

 worked out by the mathematicians from their own point of 

 view. 



2. In spite, however, of these differences of treatment, 

 there has always been some community of subject-matter in 

 the discussions upon this topic. There has almost always 



