than of genus, since definition is given in order to make a thing known, for difference is less known than genus.
Chapter 12
If however the definition of difference is assigned, examine whether the assigned difference is common to any thing else, as when it is said that an odd number is a number which has a middle, it must be defined in addition, how it has a middle. For number is common in both definitions, but instead of odd, a sentence is assumed; yet both a line and a body have a middle, though they are not odd numbers, so that this would not be the definition of the odd. Still, if that which has a middle be multifariously predicated, we must explain besides, how it possesses a middle, so that there will be either a reproof or a syllogism, that (the thing) has not been defined.
Again (observe), if that of which the definition is the sign, belongs to the number of beings, but what is under the definition does not; e. g. if white is defined colour mixed with fire, for it is impossible that the incorporeal should be mixed with body, so that it could not be colour mixed with fire, yet it is white.
Moreover, those who in (the definition of) relatives do not distinguish to what reference is made, but speak, comprehending many things, either wholly or in part enunciate falsely, as if some one should say that medicine is the science of being. For if medicine is the science of nothing which exists, it is evident that (the definition) is wholly false, but if it is of one, but not of another, it is partly false; for it is necessary (to be the science) of every thing, if it is said to be the science of being per se, and not accidentally, as is the case with other relatives, since every object of science is referred to science. Likewise, also in other things, since all
