I must be allowed to add some explanatory remarks to bring the subject home to reason—to that sluggish reason, which supinely takes opinions on trust, and obstinately supports them to spare itself the labour of thinking.
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.
Title 22, Chapter 38, section 2656f(d) of the United States Code contains this definition of terrorism:
the term “terrorism” means premeditated, politically motivated violence perpetrated against noncombatant targets by subnational groups or clandestine agents;
Discuss some of the inadequacies of this definition as a general definition of terrorism.
Discuss the adequacies of these definitions.
Chemistry is the academic discipline that studies chemical processes.
Humans are rational animals.
A religion is any system of belief that accepts an almighty and perfect God.
Time is the quantity that is measured by clocks.
Some more definitions for you to think about. These are a bit more difficult.
Sports is any activity whose primary purpose is the exercise of physical skills. (Philosopher David Papineau)
Art is the expression or application of human creative skill and imagination, typically in a visual form such as painting or sculpture, producing works to be appreciated primarily for their beauty or emotional power.
Playing a game is the "voluntary attempt to overcome unnecessary obstacles". (Bernard Suits)
See the explanations of "biscuits" and "cookies" below. If we take them as providing definitions, there is something seriously wrong. What is it?