There are several types of definiteness marking, which typically co-occur in languages. One type, is to have a non-bound definite article (as a special word class), as in German or English:
def house ‘the house’
Another type is a bound definite marker, as in Scandinavian:
house-def ‘the house’
The fundamental types of definiteness are definiteness marked on the adjective, as in Swedish:
det stor-a hus-et
DEF large-DEF house-DEF
‘the large house’
Definite marking can be obligatory, either at the end or at the beginning of a Noun Phrase, as in Bulgarian:
‘the nice book’
The ancient Indo-European languages lack definiteness, and this state has been preserved in a huge area of predominately Slavic and Indo-Aryan languages. The emergence of the various forms of definiteness began - apparently independently and with large variation even within branches of the families - already in ancient times, and escalates during the medieval period. A large part of the existing variation seems to be caused by parallel evolution. Still, the exact causes for the variation remain obscure.
Bauer, Brigitte. 2007. "The definite article in Indo-European. Emergence of a new grammatical category?" In Nominal Determination. Typology, context constratis, and historical emergence, edited by Elisabeth Stark, Elisabeth Leiss and Werner Abraham, 103-139. Amsterdam-Philadelphia: John Benjamins.
Variation in definiteness marking in historical Eurasian languages. Legens see map of modern languages above.
Probability levels of different types of definiteness marking in protolanguages, based on an evolutoinary test using the data of the DiACL database.