heidän

heidän is a Finnish possessive determiner meaning their. It is used before a noun to indicate possession by a third-person plural subject, equivalent to the English determiner their. Finnish has no articles, so heidän serves the function of signaling ownership rather than modifying the noun in other ways.

Grammatically, heidän is an attributive determiner that accompanies a noun and works with the noun’s case and number. The possessor is understood to be a plural subject speaking about multiple people. In practice, Finnish expresses the possessed object with the noun often bearing its own possessive suffix, and the combination with heidän clarifies that the possessor is plural. Common examples include: heidän talonsa on vanha (their house is old) and heidän autonsa on uusi (their car is new). The exact morphology of the possessed noun changes with case, while heidän remains the determiner indicating plural ownership.

Usage notes include that heidän is used with nouns of various genders and animacy and does not itself carry gender markers. It is typically written and spoken as a standard part of Finnish grammar, without regional variants that change its meaning, although stylistic choices can influence tone or formality in broader language use.

See also: Finnish grammar, possessive determiners, pronouns in Finnish.