How to define words (terms)

Key massage: Of important words, you should know the exact definition.


How to define a word (a term)?

Purdue’s Online Writing Lab says (, 31.12.20):


"A formal definition is based upon a concise, logical pattern that includes as much information as it can within a minimum amount of space. ... A formal definition consists of three parts:

  1. The term (word or phrase) to be defined
  2. The class of object or concept to which the term belongs
  3. The differentiating characteristics that distinguish it from all others of its class"

Sokrates and Aristotle say that a definition provides the essence of a term. The essence of something is in simple words the most important of something.


Theaitetos makes a first attempt to define the word knowledge. "Socrates raises objections to this definition. ... the definition is only an enumeration; instead of getting to the essence of knowledge, it lists only instances of knowledge." (, 01.08.21)


So a definition names the most important "characteristics that distinguish it" from other objects. I would put it this way: A definition names the most important conditions that must be met for an object to be labeled with the word (term).


A definition is like a logical rule (pattern): if something has the characteristics A and B, then it is a ... . (If the premises are true, then the conclusion is also true.)


A definition is only useful if it is simple. It cannot take into account all possible exceptions (exceptions confirm the rule). Exceptions do not matter if the definition is the most useful compared to other definitions.


"Only the fittest theories survive. Although it can never be legitimately said of a theory that it is true, it can hopefully be said that it is the best available …" (Chalmers, A. F. (1999). What Is This Thing Called Science? Open University Press, page 60)


A definition must satisfy another condition:


"A definition is the explanation of a previously unknown word with a combination of at least two previously known words." (Seffert , H. (1997) Einführung in die Wissenschaft. München: Beck Verlag, p. 49)


It makes no sense to use unknown words to define a term. If an unknown word is used in a definition, it has to be defined (explained) afterwards.


Definition: A definition ...

  • is simple - it explains an unknown word with known words.
  • names the class of object the word belongs to.
  • names the most important characteristics that distinguish the word (term) from other objects.
  • is not an enumeration - it provides the essence of a word (term).

If one criterion is not met, it is not a definition.

How to define a word / a term -