Formal Definitions
A definition is a logical technique that reveals the meaning of a term or word. It specifies the
necessary and sufficient conditions for a thing’s being a member of a specific set, enabling the
writer to set boundaries or limits that separate the term from any other term.
Definition is a important communication skill, and one that requires practice and concentration.
Particularly in technical fields, an inability to clearly define words, terms, processes, and
materials can result in both expensive waste and duplication of effort. One of the biggest
problems in student writing is a tendency to discuss words that have not been adequately
defined. A good definition consists of a formal descriptive sentence plus as many supplemental
explanatory techniques as required to make the subject clear.
A formal sentence definition consist of four components:
species (term defined) + verb + genus (general category) + differentia (what makes the term
different from other items in the category).
Species
Verb
Genus
Differentia
A triangle
is
a plane figure
with three straight bounding sides.
A carburetor
is
a mixing chamber
used in gasoline engines to produce
efficient vapor of fuel and air.
It is important to carefully limit the genus. The narrower the genus, the more exact the definition
will be. Consider the following examples. Which gives a clearer defintion of the term?
Species
Verb
Genus
Differentia
A rifle
is
a dangerous object
that shoots bullets.
A rifle
is
a firearm
with a long, narrow barrel.
What is wrong with this definition?
Species
Verb
Genus
Differentia
A belt
is
an article of clothing
that holds up pants.
At the same time, the genus should not be stated too narrowly.
Species
Verb
Genus
A chair
is
a four-legged piece of
furniture
Differentia
on which people sit
Be careful not to repeat any form of the species in the differentia. To do so is to construct a
circular definition, which does not clarify the writer’s meaning. Circular definitions would include
the following:
Species
Verb
Genus
Differentia
Comatose
is
a state
of being in a coma.
Fertilization
is
the process
of fertilizing an object.
Avoid the words “when” or “where” after the verb to be. Using these words prevents the clear
statement of the genus as a noun phrase. Which definition is clearer?
Species
Verb
Genus
Differentia
A crypt
is where
people
are buried.
A crypt
is
a subterranean chamber in which people are buried.
Not only is the first definition awkwardly written, but it could also describe cemeteries and
mausoleums. Here is another example:
Species
Verb
Genus
Differentia
Osmosis
is when
fluid
passes through a membrane.
Osmosis
is
a process
in which fluid passes through a
membrane.
Species
Verb
Genus
Differentia
Nancy Swisher
is
a teacher
at NC State
Nancy Swisher
is
a Coker College
alumna
who teaches at NC State.
(Name)
is
a student from China
who is majoring in EE.
(Name)
is
is a Chinese student
majoring in EE
who is on the swim team.
Consider:
Sources: Dynamic Communication for Engineers by Riuchard H. McCuen, Peggy A. Johnson and Cynthia
Davis; Wikipedia