którymi

"którymi" is the instrumental plural form of the Polish interrogative and relative pronoun "który" (English: “which,” “that”). As an instrumental case, it is used when the pronoun functions as the object of a preposition that requires the instrumental, or when it denotes means, manner, or accompaniment. The form appears in both questions and relative clauses, linking a noun phrase to a verb or preposition.

In interrogative sentences, "którymi" introduces a query about the means or instrument by which an action is performed, e.g., “Jakimi środkami leczy się chorobę?” (What means are used to treat the disease?). In relative clauses, it connects a subordinate clause to a antecedent, for example: “Z narzędziami, którymi pracujemy, jesteśmy zadowoleni” (We are satisfied with the tools with which we work).

Morphologically, "którymi" derives from the base stem "który-" plus the instrumental plural ending "-mi". The pronoun declines across all seven Polish cases, with distinct forms for singular, plural, masculine, feminine, and neuter genders. The instrumental plural is the only plural form that ends in "-mi"; the singular instrumental is "którym" (masc./neut.) or "którą" (fem.).

Etymologically, "który" traces back to Proto‑Slavic *kъtъri, related to other Slavic languages (Czech "který", Russian "который") and ultimately to the Indo‑European root *kʷi‑ “who, what”. The instrumental plural "którymi" therefore shares cognates across Slavic languages, although the exact form varies (e.g., Czech "kterými").

In contemporary Polish, "którymi" is frequently employed in formal, academic, and technical writing, where precise reference to instruments or means is required. It is also common in everyday speech when asking about tools or methods.