The sixth argument:

A definition consists of words. Words do not convey their meaning to a listener unless he has already conceived of the meanings of their individual terms by means other than words. For a single term does not convey its meaning to a listener unless he knows that it has been assigned to that meaning, and he cannot know this until he knows the meaning itself. Conceiving of simple meanings must therefore precede understanding what is intended by words. If those conceptions were themselves acquired through words, circularity would necessarily follow.

This is a matter of direct experience. Unless someone using a single term makes its meaning clear to the listener so that he grasps it through his senses or reflection, it is inconceivable that the listener should grasp it through a statement composed of a genus and a differentia.

The seventh argument:

A definition distinguishes and differentiates the thing defined from everything else. It thus accomplishes what names accomplish by distinguishing and differentiating the thing named from everything else. There is no doubt that this serves to distinguish. It does not, however, furnish a conception of a thing’s real nature. Definitions may nevertheless spell out in detail what a name indicates in summary, but this has nothing to do with apprehending the thing’s real nature.

The condition for this is that the attributes be essential. Rather, it is akin to division: defining the whole is like dividing it into its particulars. This will become clear.