Modern Definitions: the Kinds

In one line

Modern logic classifies definitions by what they are trying to do: report a usage, create one, sharpen one, express a theory, or change an attitude.

In the wording a student can write in an examination: modern logic distinguishes five kinds of definition. A stipulative definition assigns a meaning by declaration; a lexical definition reports an existing usage; a précising definition reduces the vagueness of an existing usage for a particular purpose; a theoretical definition proposes an account of the nature of the thing; and a persuasive definition is framed so as to influence attitude.

Why the classification is by purpose

Because the traditional account had only one kind, and judged every definition by one set of rules. That produced a difficulty at once: a definition that creates a usage cannot be criticised for departing from usage, and a definition that reports one cannot be criticised for failing to sharpen it. A single standard cannot be applied to five different jobs.

So the modern account asks first what the definition is for, and the rules that apply follow from the answer. That is the same move made at sequence 540 and it is the whole basis of the classification.

Stipulative definitions

What it does. Assigns a meaning to a term by declaration, either to a newly coined word or to an existing word given a new sense for a stated context.

How it is judged. Not by truth. A stipulative definition is neither true nor false, because it reports nothing; it makes something so by declaring it. What it can be is useful or useless, convenient or clumsy, clear or unclear.

Where the law uses it. Constantly, and in a specific place: the opening words of a definition clause. "In this Act, unless the context otherwise requires, 'appropriate Government' means..." is a stipulation. It is not a claim about how anybody uses the expression, and it cannot be answered by showing that the expression is used differently elsewhere.

The reason this matters. An argument that a statutory definition is "wrong" because it departs from the ordinary meaning of the word is an argument that misunderstands what the clause is doing. What can be argued is that a person or thing falls outside the stipulated words, or that the context otherwise requires, which is what the standard opening formula expressly allows.

Lexical definitions

What it does. Reports how a term is in fact used in a language or in a community.

How it is judged. By truth. A lexical definition can be right or wrong, because it makes a claim about usage, and it is refuted by producing uses it fails to cover or wrongly covers. This is the one kind of definition to which the "too wide or too narrow" fallacies of sequence 560 apply in their full strength.