заче́м vs для чего́

zachem vs dlya chego — why vs for what purpose

What it really means

Заче́м asks about the purpose or intended benefit of an action: “what for?” or “why do you need it?” It often concerns a deliberate action and can sound like a request for justification. Для чего́ has the same basic meaning but is more explicit and somewhat more formal or bookish; it is especially natural when identifying the function or purpose of something.

Neither word is the ordinary choice for asking about a cause. For a reason or explanation, use почему́: Почему́ ты опоздал? (“Why were you late?”). Use заче́м for a person’s goal and для чего́ for a stated purpose, function, or formal question about intended use.

Examples in natural speech

Заче́м ты купил новый телефон?
Why did you buy a new phone?
Заче́м тебе́ нужна́ эта кни́га?
What do you need this book for?
Для чего́ ну́жна э́та кнопка?
What is this button for?
Для чего́ вы испо́льзуете э́ту про́грамму?
What do you use this program for?
Почему́ ты не позвони́л вчера́?
Why didn't you call yesterday?

Common mistakes

Do not automatically translate every English “why” as заче́м. Use почему́ for a cause or explanation, заче́м for a goal, and для чего́ when asking explicitly about purpose or function. Remember that чего́ is genitive after для.

Memory tip

Заче́м looks forward to a goal; почему́ looks backward to a cause; для чего́ labels a purpose clearly.

Frequently asked questions

Are заче́м and для чего́ interchangeable?

Often yes when asking about purpose, but для чего́ is more explicit and can sound more formal, while заче́м is more conversational.

Can заче́м sound critical?

Yes. Depending on intonation, Заче́м ты это сделал? can sound like “Why on earth did you do that?”

Which word means “why” in Почему́ ты устал?

Почему́ is correct because the question asks for the cause of being tired, not the intended purpose.

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