Definition.  One of the simplest ways of explaining is to define a term.  Dictionary definitions are familiar to everyone.  In a great many instances the dictionary definition is by means of synonyms.  While this is a convenient, easy method it is seldom exact.  Why?  Recall what you learned concerning the meanings of synonyms.  Do they ever exactly reproduce one another’s meanings?  There is always a slight degree of inaccuracy in definition by synonym, sometimes a large margin of inexactness.  Is the following a good definition?

A visitor to a school began his address:  “This morning, children, I propose to offer you an epitome of the life of St. Paul.  It may be perhaps that there are among you some too young to grasp the meaning of the word epitome. Epitome, children, is in its signification synonymous with synopsis!”

    London Tid-Bits

Logical Definition.  An exact definition is supplied by the logical definition.  In this there are three parts—­the term to be defined, the class (or genus) to which it belongs, and the distinguishing characteristics (differentia) which mark it off from all the other members of that same class.  You can represent this graphically by inclosing the word term in a small circle.  Around this draw a larger circle in which you write the word class.  Now what divides the term from the class in which it belongs?  Indicate the line around the term as distinguishing characteristics, and you will clearly see how accurate a logical definition is.  The class should be just larger than the term itself.  The main difficulty is in finding exact and satisfying distinguishing characteristics.  There are some terms which are so large that no classes can be found for them.  Others cannot be marked by acceptable distinguishing characteristics, so it is not possible to make logical definitions for all terms.  Consider such words as infinity, electricity, gravity, man.

The words of the definition should be simple, more readily understood than the term to be defined.

Term Class Distinguishing characteristics

A biplane is an airplane with two sets of supporting
                                         surfaces.

A waitress is a woman who serves meals.

Narration is that form of discourse which relates events.

A word is a combination of suggesting an idea.
              letters
A dictionary is a book of definitions.

A corporal is an army officer just higher than a private.

EXERCISES

1.  Make logical definitions for the following: 

A dynamo A circle A hammer
A curiosity Lightning A trip-hammer
Moving picture camera Democracy A lady
Curiosity An anarchist A Lady
A door A sky-scraper Man