  The “Conversion of Relations” does not mean what it might be supposed to mean; it has nothing to do with what Kant called “the wholesome art of persuasion.” What concerns us here is the convertibility of a logical relation. If A has a certain relation R to B, the relation of B to A, which may be denoted by R, is called the converse of R. As De Morgan “Teacher: ‘Now, boys, Shem, Ham and Japheth were Noah’s sons; who was the father of Shem, Ham and Japheth?’ No answer. “Teacher: ‘Boys, you know Mr. Smith, the carpenter, opposite; has he any sons?’ “Boys: ‘Oh! yes, sir! there’s Bill and Ben.’ “Teacher: ‘And who is the father of Bill and Ben Smith?’ “Boys: ‘Why, Mr. Smith, to be sure.’ “Teacher: ‘Well, then, once more, Shem, Ham and Japheth were Noah’s sons; who was the father of Shem, Ham and Japheth?’ “A long pause; at last a boy, indignant at what he thought the attempted trick, cried out: ‘It couldn’t have been Mr. Smith.’ These boys had never converted the relation of father and son....”
|
|
