70 THE PRINCIPLES OF SCIENCE. [CHAP. 



saint and a philosopher ? Such a construction would be 

 ridiculous." 



I discuss this subject fully because it is really the point 

 which separates my logical system from that of Boole. 

 In his Laws of Thought (p. 32) he expressly says, 

 " In strictness, the words ' and,' ' or,' interposed between 

 the terms descriptive of two or more classes of objects, 

 imply that those classes are quite distinct, so that no 

 member of one is found in another." This I altogether 

 dispute. In the ordinary use of these conjunctions we do 

 not 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 that they are 

 distinct. If 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. 



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, " Uustain'd 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 anadera, or 

 an anadem a wreath, or whether they are quite distinct or 

 quite the same. From Darwin's Origin of Species, I 

 take the expression, " When we see any part or organ 

 developed in a remarkable degree or manner" In this, or 

 is ussd twice, and neither time exclusively. For if part 

 and organ are not synonymous, at any rate an organ is a 

 part. And it is obvious that a part may be developed at 

 the same time both in an extraordinary degree and an 

 extraordinary manner, although such cases may be com- 

 paratively rare. 



From a careful examination of ordinary writings, it will 

 thus be found that the meanings of terms joined by "and," 

 " or " vary from absolute identity up to absolute contrariety. 

 There is no logical condition of distinctness at all, and 

 when we do choose exclusive alternatives, it is because 

 our subject demands it. The matter, not the form of an 



