który

Który is a Polish interrogative and relative pronoun and determiner used to specify an item from a defined set or to introduce a relative clause describing a noun. It agrees with the noun it modifies in gender, number and case, and has distinct forms for singular and plural, as well as for different cases.

In questions, który asks for a specific choice, for example: "Który dzień jest dziś?" (Which day is today?), "Która książka należy do ciebie?" (Which book is yours?). In the plural or when referring to people, forms such as "którzy" (masculine personal plural) and "które" (for neuter and most non-personal references) appear. The form changes to match the noun's gender and the required case in the sentence, and auxiliary forms like "którego," "której," "któremu" appear in genitive, dative, or other cases.

As a relative pronoun, który introduces a clause that provides additional information about a noun mentioned earlier. For example: "To jest książka, którą przeczytałem" (This is the book that I read) uses the relative form with the noun it modifies; other forms agree with gender and case, as in "kobieta, która przyszła" (the woman who came). The phrase "o którym mowa" shows a prepositional use, where the form adapts to the case required by the preposition.

Etymologically, który derives from the Proto-Slavic root used in related languages (e.g., Russian который, Czech který, Polish ktory/który). It functions alongside other question and relative pronouns to express selection and specification in discourse.