Definition & Meaning of "instrumental case"

What is the "instrumental case"?

The instrumental case is a grammatical case used to indicate the means or instrument by which an action is performed. It shows how something is done or the tool used to achieve an action. The instrumental case is present in several languages, such as Russian and Polish, where it alters the form of nouns to express this relationship. For example, in Russian, the word for "book" changes from "книга" (kniga) to "книгой" (knigoy) when indicating "with the book." The instrumental case helps clarify the methods or instruments involved in actions within a sentence.