Defining “Definition”

How do we define “definition”? It is somewhat disappointing to learn that there is no one definition, acceptable to most, if not all, logicians. This surprise will soon disappear when we notice that several functions performed as a way of clarifying expressions (or statements), either completely with words or with combinations of words and symbols, have all been considered legitimate acts of defining. Consequently, there are many variations of the meaning of “definition.”

Having accepted this situation, we will mention (rather, quote somewhat freely) a few variations, meant to give the breadth of the word “definition,” though not its depth.

• A real definition involves two sets of expressions, each with a meaning of its own, and these mean­ings are equivalent if the definition is true.²
• A definition is a phrase signifying a thing’s essence. (Furthermore,) A definition contains two terms as components, the genus and the A genus is what is predicated in the category of essence of a number of things exhibiting differences in kind, and the differentia is that part of the essence that distinguishes the species from the other species in the same genus.

—Attributed to Aristotle³

Four of the following definitions, (C) through (F), appear within a span of six pages in one book.⁴ The rest are taken from other sources.

• A definition is a way of restricting the meaning of a term that has several meanings to prevent ambi­guity and equivocation.
• A definition is true . . . if the defining term has the same designation as the term to be defined.
• Definition is a rule of substitution.
• “Definition” = statement that one term has the same designation as another term.
• A definition is the statement of the meaning of a word, etc.
• A definition is a brief description of a thing by its properties.
• A definition is an explanation of the meaning of a word or expression.

Source: Srinagesh K (2005), The Principles of Experimental Research, Butterworth-Heinemann; 1st edition.