in terms of similarity. Thus it is the distinctive [35] mark of quantity that it can be called equal and unequal. Those things are called relative, which, being either said to be of something else or related to something else, are explained by reference to that other thing. For instance, the word ‘superior’ is explained by reference to something else, for it is superiority over something else that is meant. Similarly, the expression ‘double’ has this external reference, for it is the double of