tion of rodent by saying, "A rodent is a beaver," because the term
beaver does not include all rodents. We must also take care to choose for
the genus some term familiar to the reader, because the object of the
definition is to make the meaning clear to him.

The chief difficulty of framing logical definitions arises in the
selection of differentia. In many cases it is not easy to decide just what
characteristics distinguish one member of a class from all other members
of that class. We all know that iron is a metal, but most of us would
find it difficult to add to the definition just those things which
distinguish iron from other metals. We may say, "A flute is a musical
instrument"; so much of the definition is easily given. The difficulty
lies in distinguishing it from all other musical instruments.

EXERCISES

_A._ Select proper differentia for the following:--

|
TERM TO BE DEFINED | CLASS (Genus) | DISTINGUISHING
| | CHARACTERISTIC
| | _(Differentia)_
| |
1. Narration | is that form of discourse | ?
| |
2. A circle | is a portion of a plane | ?
| |
3. A dog | is an animal | ?
| |
4. A hawk | is a bird | ?
| |
5. Physiography | is the science | ?
| |
6. A sneak | is a person | ?
| |
7. A quadrilateral | is a plane figure | ?
| |
8. A barn | is a building | ?
| |
9. A bicycle | is a machine | ?
| |
10. A lady | is a woman | ?

_B._ Give logical definitions for at least four words in the list below.

1. Telephone.

2. Square.

3. Hammer.

4. Novel

5. Curiosity.

6. Door.

7. Camera.

8. Brick.

9. Microscope.

+161. Inexact Definitions.+--If the distinguishing characterist