The anaphoric type of unique identifiability, which is discourse-based, involves the use of the prenominal definite determiner di. Where the unique identifiability of a referent is based on cultural or pragmatic knowledge, it is signalled by a null definite determiner. Finally, the definite article can also be used with generic reference. See Kouwenberg (2007) for discussion.
Source: Kouwenberg 2007: 442