What makes a thing a thing and what makes your definition of a thing a good one?
*Adapted from a third year Ethics course by Dr. Mano Daniel*

The Definiendum: ex. a cat (what we are defining)
The Definien: the actual definition

There are five features that a good definition should have in order for it to be a good definition.

1. The definien must not be too broad. It can not exclude things that should be included. Ex: “A chair is a piece of furniture used to sit on.” This definition is too broad because it allows things that shouldn’t be included to be included such as a sofa bed, which would fit the definition.
2. The definien must not be too narrow, that is it should not include things that should be excluded. Ex: “A chair is a piece of furniture with four legs and is made of wood.” This definition is too narrow because not all chairs have four legs, or are made of wood, and therefore it includes things that should be excluded.
3. The definien should state the most important attributes of the defieniendum; the “essence” of the object/thing. Ex: Defining a car in terms of metals used to create the car does not capture the purpose of a car, which is to drive/move around in, etc.
4. The defienien should not be circular. That is, the reader shouldn’t have to know the definition of the word already in order to understand the definition. Ex: “A swimmer is a person that swims.” – you would have to understand what swimming is in order to understand this definition.
5. The defienien should not be obscure, it should be understood by almost anyone. Ex: “A chair is an ontologically stable, space-time existent, constructed from natural or artificial materials and designed for human beings in non-reclining pose.”