Formal Definitions

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

Differentia

A chair

is

a four-legged piece of

on which people sit

furniture

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.

Consider:

Species Nancy Swisher Nancy Swisher

Verb is is

(Name)

is

(Name)

is

Genus

a teacher

a Coker College alumna

a student from China

is a Chinese student majoring in EE

Differentia at NC State who teaches at NC State.

who is majoring in EE. who is on the swim team.

Sources: Dynamic Communication for Engineers by Riuchard H. McCuen, Peggy A. Johnson and Cynthia Davis; Wikipedia

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