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 &, is called the converse of R. As De Morgan 1 remarked, this conversion may sometimes present difficulties. The following is De Morgan's example :

" Teacher: ' Now, boys, Shem, Ham and Japheth were Noah's sons; who was the father of Shem, Ham and Japheth ? ' No answer.