84 THE PRINCIPLES OF SCIENCE. 



dispute. In the ordinary use of these conjunctions we do 

 riot necessarily join distinct terms only ; and when terms 

 so joined do prove to be logically distinct, it is by virtue 

 of a tacit premise, something in the meaning of the names 

 and our knowledge of them, which teaches us they are 

 distinct. And when our knowledge of the meanings of the 

 words joined is defective it will often be impossible to 

 decide whether terms joined by conjunctions are exclusive 

 or not. 



Take, for instance, the proposition 'A peer is either 

 a duke, or a marquis, or an earl, or a viscount, or a baron/ 

 If expressed in Professor Boole's symbols, it would be 

 implied that a peer cannot be at once a duke and marquis, 

 or marquis and earl. Yet many peers do possess two or 

 more titles, and the Prince of Wales is Duke of Cornwall, 

 Earl of Dublin, and Baron Renfrew. If it were enacted by 

 parliament that no peer should have more than one title, 

 this would be the tacit premise which Professor Boole 

 assumes to exist. Nor is the restriction true of more 

 common terms. 



In the sentence * Repentance is not a single act, but a 

 habit or virtue/ it cannot be implied that a virtue is not a 

 habit ; by Aristotle's definition it is. 



Milton has the expression in one of his sonnets, 

 ' Unstained by gold or fee/ where it is obvious that if 

 the fee is not always gold, the gold is meant to be a fee 

 or bribe. 



Tennyson has the expression 'wreath or anadem/ Most 

 readers would be quite uncertain whether a wreath may 

 be an anadem, or an anadem a wreath, or whether they 

 are quite distinct or quite the same. 



From Darwin's ' Origin/ I take the expression, ' When 

 we see any part or organ developed in a remarkable 

 degree or manner.' In this, or is used twice, and neither 

 time disjunctively. For if part and organ are not 



