A definition describes a concept. A concept has many characteristics. The process of abstraction occurs when we consider the characteristics of a concept individually (or, at least this is one way in which the term "abstraction" is used). Very often, the characters considered the most when doing definitions are those which describe the essence of the concept. Consider, for instance, the traditional Aristotelian formula for a definition:
Definition = Genus + Specific Difference
In the historical literature about definitions, emphasis was put on the specific difference as being the essential characters of a concept. This may serve the philosophers' purposes, but it ignores the problem of identification, and the need to consider identifying characteristics in a definition.
Suppose I want to define the concept of Exit Row in a plane. Let's try to do so using Aristotle's method.
"A row of seats that provides emergency access to the outside of a plane"
A bit provisional perhaps, but is does begin to convey the essence of an Exit Row. But how do flight attendants identify an Exit Row to passengers when they give the safety briefing? It goes something like this:
"For those of you seated in a row marked by the sign 'No Children In This Row'..."
The essence of an Exit Row is not that it is an area of a plane that is kept free of children. The essence is that it is a point of emergency egress from a plane. Only competent adults are thought to be capable of opening an emergency exit, so only they are permitted to sit in an Exit Row.
However, it fairly easy for a passenger to identify an Exit Row based on finding a sign saying 'No Children in This Row'. The sign functions as an identifying characteristic.
An identifying characteristic is a characteristic that easily permits the identification of an instance of a concept with the correct concept.
Identification is a distinct use case (possibly a set of distinct use cases) that definitional work must support. It is not automatically supported by finding essential characteristics, as our example of Exit Row shows. We shall return to the topic of identification in the future. Frankly, identification seems to be poorly supported in the literature of definitions. Yet it is something we are challenged with every day.
If practical work with a concept involves identification of instances, the definition of the concept must support this work by clearly listing identifying characteristics and saying how they should be used in identification.
Definition = Genus + Specific Difference
In the historical literature about definitions, emphasis was put on the specific difference as being the essential characters of a concept. This may serve the philosophers' purposes, but it ignores the problem of identification, and the need to consider identifying characteristics in a definition.
Suppose I want to define the concept of Exit Row in a plane. Let's try to do so using Aristotle's method.
"A row of seats that provides emergency access to the outside of a plane"
A bit provisional perhaps, but is does begin to convey the essence of an Exit Row. But how do flight attendants identify an Exit Row to passengers when they give the safety briefing? It goes something like this:
"For those of you seated in a row marked by the sign 'No Children In This Row'..."
The essence of an Exit Row is not that it is an area of a plane that is kept free of children. The essence is that it is a point of emergency egress from a plane. Only competent adults are thought to be capable of opening an emergency exit, so only they are permitted to sit in an Exit Row.
However, it fairly easy for a passenger to identify an Exit Row based on finding a sign saying 'No Children in This Row'. The sign functions as an identifying characteristic.
An identifying characteristic is a characteristic that easily permits the identification of an instance of a concept with the correct concept.
Identification is a distinct use case (possibly a set of distinct use cases) that definitional work must support. It is not automatically supported by finding essential characteristics, as our example of Exit Row shows. We shall return to the topic of identification in the future. Frankly, identification seems to be poorly supported in the literature of definitions. Yet it is something we are challenged with every day.
If practical work with a concept involves identification of instances, the definition of the concept must support this work by clearly listing identifying characteristics and saying how they should be used in identification.
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