Rules for Definitions
A Genus and a Differentia

A definition should include a genus and a differentia.

Example:

Humans are rational animals.

The term "animal" names the wider class to which humans belong; it classifies us as a species of the genus ANIMAL.

The term "rational" specifies an attribute that distinguishes us from other species of the same genus. This part of the definition is called the differentia--it differentiates humans from other animals.


A Genus and a Differentia | Neither Too Broad Nor Too Narrow |
Essential Attributes | Avoid Circularity | Avoid Negative Terms | Avoid Vagueness

Rules for Definitions

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