definition in logic


Definition of definition

A definition is the statement of the connotation of a term which clearly expresses the meaning of an idea or term.

Purpose of a definition:

  • To increase the vocabulary.
  • To eliminate ambiguity.
  • To clarify meaning.
  • To explain theoretically.

A definition is must contain two parts, namely; the definiendum and the definiens.

The defiendum refers to the term or symbols being defined; while the definiens refers to the word or words used in defining.  The kinds of definition are:

  • Stipulative Definition: this is the kind of definition which gives meaning to a brand new term when introduced. E.g. “mbutoku” means foolish person.
  • Ostensive definition: this is a kind definition we make the by pointing out the term being defined or enuminarating its examples. For example: a philosopher is someone like Socrates.
  • Nominal definition: this is the kind of definition which explains the meaning of a word by breaking their into component parts. For example: metaphysics can be broken into Meta which means beyond and physika which means natural.
  • Theoretical definition: this is the intentional definition which attempts to provide a deeper understanding of the nature of a thing.
  • Lexical definition: this is a definition which explains the conventional intension of a term, usually by stating the dictionary meaning of the word.
  • Analytical definition: this Is the kind of definition that states the nature of a thing by stating its genus and species to which it belongs. E.g. A spinster is an unmarried woman.
  • Synonymous definition: this is the which give the meaning of a term by introducing another term with the same meaning


  1. A Good Definition must be Adequate: this means that the definiens must be equal to the defiendum.

A definition is “too wide”, when the definiens denotes more things than the definiendum. For example: money means wealth.

A definition is “too narrow” when the definiens denote less things than the definiendum. For example a computer is used for typing. When a definition is too wide or narrow it commits the fallacy of “Incongruous definition”

Rules of definition Fallacies committed
  A good definition must be precise and clear Fallacy of obscure definition. E.g. By defining happiness as wellbeing of the soul.
A definition should not be circular Fallacy of circular definition e.g. A teacher is someone who teaches.
A definition should not be negative. Fallacy of negative definition.
A Definition should be per genus et differentiam Fallacy of extraneous definition E.g. A Kitten is a young cat

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