The criteria for evaluating definitions depends on the kind of definition we are considering. With reportive definition, it is important that the definition provided correctly captures the usage of the term that is defined. In particular, this means that the definition should be neither too wide (or too broad) nor too narrow.
- A definition is too wide if the definiens applies to things that the definiendum does not apply to. In other words, the definition includes things that it should not. For example, defining a chair as a piece of furniture for sitting is too wide because a bench is not a chair but it satisfies the definition.
- A definition is too narrow if the definiens fails to include things to which the definiendum applies. In other words, the definition fails to include things that it should. Consider the definition of religion as any belief system that includes worshiping a god who created the universe. This definition is too narrow since it excludes religions that do not postulate a creator, such as Jainism and certain versions of Buddhism and Daoism.
- it is important to note that a definition can be both too wide and too narrow, e.g. chair = a piece of furniture for sitting which has four legs.
In giving a stipulative definition, since we are introducing a new meaning, the question of whether the definition is too broad or too narrow does not arise. But it is important that the definien should avoid circularity, inconsistency and obscurity.
- An example of a circular definition: temperature is the physical quantitiy that is measured by a thermometer. This definition might help someone understand what the word "temperature" means in English, but it is circular as a definition. This is because there is no way to explain what a thermometer is without using the concept of temperature.