The roots of direct reference 3

Argument Three.  A definition must provide the genus of the thing defined, and the specific difference by which the species defined is distinguished from every other species belonging to that kind. Thus only a species can be defined.  But a proper name be defined, for individuals are not species.  They have no specific difference, and can only be distinguished by the proper name itself.  Thus the meaning of a proper name is the individual it names.

Suggested by Reid again.  Of the Intellectual Powers, pp 219-20.  See also Argument 1, argument 2.