Sentence:  To do this , it is sufficient to point out that if the <WSD>principle</WSD> in terms of which alternatives are to be conceived is such as to exclude more than two , then the question of a `` third '' possibility is a meaningless question . 
Meaning of the word marked with <WSD> tags:  (law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature)