Defining rehabilitation: An exploration of why it is attempted, and why it will always fail

Over 187 definitions of rehabilitation exist, none widely agreed or used. Why?

Words represent a core concept, with a penumbra of associated meanings. A word means what is agreed among those who use it. The precise meaning will vary between different groups. Words evolve, the meaning changing with use. Other words may capture some of the concepts or meanings.

A definition is used to control the unstable, nebulous meaning of a word. It delineates, creating a boundary. A non-binary spectrum of meaning is transformed into binary categories: rehabilitation, or not rehabilitation. In clinical terms, it is a diagnostic test to identify rehabilitation. There are many different reasons for categorising something as rehabilitation. Each will need its own definition.

The ability of a definition to distinguish cases accurately must be validated by comparison with 'the truth'. If there were an external 'true' test to identify rehabilitation, a definition would not be needed. As with most concepts, the only truth is agreement by people familiar with the required distinction. Any definition will generate misclassification. People familiar with the required distinction will also need to resolve mis-categorisation.

An alternative is a 'descriptive definition', listing features over several domains which must be present. This fails logically. Rehabilitation is an emergent concept, more than the sum of its parts.

A useful definition cannot be achieved because no definition will cover all needs, and a specific definition for a purpose will misclassify some cases.