Lack of clarity in meaning can hinder good reasoning and obstruct communication. One way to make meaning clearer is to use definitions. A definition is made up of two parts: the definiendum and the definiens. The definiendum is the term that is to be defined, whereas the definiens is the group of words or concepts used in the definition that is supposed to have the same meaning as the definiendum. For example, bachelor is defined as an unmarried man. The word “bachelor” is the definiendum, and “an unmarried man” is the definiens. We now look at four main kinds of definitions.
A reportive definition is also known as a lexical definition. It reports the existing meaning of a term. This includes the bachelor example above, or the definition of prime number as any integer greater than one and divisible only by one and itself. A reportive definition should capture the correct usage of the term that is defined.
A stipulative definition is not used to explain the existing meaning of a term. It assigns a new meaning to a term, whether or not the term has already got a meaning. If the stipulative definition is accepted, then the term is used in the new way that is prescribed. For example, we might stipulate “KFC” to mean “Korean-style Fried Chicken”. Once the definition is accepted,we can then say things like, “We are going to cook KFC for dinner tonight”.
A precising definition is used to make the meaning of a term more precise for some specific purpose. For example, a bus company might want to give discounts to elderly passengers. But simply declaring that the elderly can pay a reduced fare will lead to many disputes, since it isnot clear how old one should be to qualify as an elderly person. So one might define “an elderlyperson” to mean any person of age 65 or above. This is of course one among many possible definitions. A precising definition might be seen as a combination of reportive and stipulative definition.
Precising definitions are very important in drawing up laws and regulations. We might want to eliminate or punish sexual harassment, but we need a good definition of sexual harassment to clarify what is appropriate and what is not. A biology professor who makes his students unhappy by giving a surprise exam on sexual reproduction should better not be counted as sexual harassment under any such definition.
Precising definitions can also be used to resolve disputes that involve some key concepts whose meanings might not be clear enough. Suppose two people are arguing whether animals such as birds or apes possess language. To resolve this dispute, we need to be more precise as to what is meant by language. If by language we refer to any system of communication, then obviously birds and other animals do make use of languages. On the other hand, “language” might be used in a different sense, referring to more sophisticated communication systems with a recursive syntax. If this is what is meant, the communication systems of many animals would not qualify as language.
A persuasive definition is any definition that attaches an emotive connotation to a term when it actually none. The connotation can be either positive or derogatory. For example, someone against abortion might define “abortion” as the murder of an innocent child inside the womb.This definition carries a negative connotation, as the term murder suggests that abortion is wrongful killing, and it also assumes that the aborted fetus is already a person. This definition might make a useful rhetorical tool, but it is a biased and inappropriate definition. Whether abortion is wrong should be determined by careful analysis and argument, and not to be stipulated by a definition.
The criteria for evaluating definitions depend on the kind of definition we are considering. With reportive definition, it is important that the definition correctly captures the usage of the term that is defined. In particular, the definition should be neither too wide nor too narrow.
- A definition is too wide (or too broad) if the definiens applies to things that the definiendum does not apply to. For example, defining an airplane as a flying machine is too wide since helicopters are also flying machines but they are not airplanes.
- A definition is too narrow if the definiens fails to apply to things to which the definiendum applies, e.g. defining a triangle as a plane figure with three equal straight sides.
- Notice that a definition may be both too wide and too narrow at the same time. Consider the definition of a chair as a piece of furniture with four legs for people to sit on. The definition is too narrow as some chairs might not have four legs. It is also too wide because a sofa with four legs might still not be a chair.
The question of whether a definition is too broad or too narrow does not arise with stipulative definitions, since the definition is not meant to capture existing usage. But it is important that the definition should avoid circularity, inconsistency and obscurity.