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It is evident that every Member of a Species is also a Member of the Genus out of which that Species has been picked, and that it possesses the Differentia of that Species. Hence it may be represented by a Name consisting of two parts, one being a Name representing any Member of the Genus, and the other being the Differentia of that Species. Such a Name is called a ‘Definition’ of any Member of that Species, and to give it such a Name is to ‘define’ it.

[Thus, we may define a “Treasure” as a “valuable Thing.” In this case we regard “Things” as the Genus, and “valuable” as the Differentia.]

The following Examples, of this Process, may be taken as models for working others.

[Note that, in each Definition, the Substantive, representing a Member (or Members) of the Genus, is printed in Capitals.]

1. Define “a Treasure.”

Ans. “a valuable Thing.”

2. Define “Treasures.”

Ans. “valuable Things.”

3. Define “a Town.”

Ans. “a material artificial Thing, consisting of houses and streets.”

4. Define “Men.”

Ans. “material, living Things, belonging to the Animal Kingdom, having two hands and two feet”;

or else

“Animals having two hands and two feet.”

5. Define “London.”

Ans. “the material artificial Thing, which consists of houses and streets, and has four million inhabitants”;

or else

“the Town which has four million inhabitants.”

[Note that we here use the article “the” instead of “a”, because we happen to know that there is only one such Thing.

The Reader can set himself any number of Examples of this Process, by simply choosing the Name of any common Thing (such as “house,” “tree,” “knife”), making a Definition for it, and then testing his answer by referring to any English Dictionary.]