Page - 298 - in The Complete Aristotle

same genus are simultaneous by nature and ‘odd’ and ‘even’ are such terms: for both are differentiae of number. Likewise also, see if he has defined a superior through a subordinate term, e.g. ‘An “even number” is “a number divisible into halves”’, or ‘”the good” is a “state of virtue” ‘. For ‘half’ is derived from ‘two’, and ‘two’ is an even number: virtue also is a kind of good, so that the latter terms are subordinate to the former. Moreover, in using the subordinate term one is bound to use the other as well: for whoever employs the term ‘virtue’ employs the term ‘good’, seeing that virtue is a certain kind of good: likewise, also, whoever employs the term ‘half’ employs the term ‘even’, for to be ‘divided in half’ means to be divided into two, and two is even. < div id=“section54” class=“section” title=“5”> 5 Generally speaking, then, one commonplace rule relates to the failure to frame the expression by means of terms that are prior and more intelligible: and of this the subdivisions are those specified above. A second is, see whether, though the object is in a genus, it has not been placed in a genus. This sort of error is always found where the essence of the object does not stand first in the expression, e.g. the definition of ‘body’ as ‘that which has three dimensions’, or the definition of ‘man’, supposing any one to give it, as ‘that which knows how to count’: for it is not stated what it is that has three dimensions, or what it is that knows how to count: whereas the genus is meant to indicate just this, and is submitted first of the terms in the definition. Moreover, see if, while the term to be defined is used in relation to many things, he has failed to render it in relation to all of them; as (e.g.) if he define ‘grammar’ as the ‘knowledge how to write from dictation’: for he ought also to say that it is a knowledge how to read as well. For in rendering it as ‘knowledge of writing’ has no more defined it than by rendering it as ‘knowledge of reading’: neither in fact has succeeded, but only he who mentions both these things, since it is impossible that there should be more than one definition of the same thing. It is only, however, in some cases that what has been said corresponds to the actual state of things: in some it does not, e.g. all those terms which are not used essentially in relation to both things: as medicine is said to deal with the production of disease and health; for it is said essentially to do the latter, but the former only by accident: for it is absolutely alien to medicine to produce disease. Here, then, the man who renders medicine as relative to both of these things has not defined it any 298