Someone closes the window halfway through dinner. In English, “Why did you close the window?” could mean that you felt a draft and wondered if they did too. It could also mean that you’re trying to work out what closing it was supposed to accomplish. The person answering has to take a small guess.
In Russian, you can give them a clue before you get to the verb.
Почему ты закрыл окно? — Why did you close the window?
Потому что стало холодно. — Because it got cold.
Зачем ты закрыл окно? — What did you close the window for?
Чтобы не было слышно машин. — So we wouldn’t hear the cars.
Same window, same action. The first answer tells you what prompted it. The second tells you what the person wanted to achieve. That’s the difference between почему and зачем, and it matters most in conversations where either question would make sense.
Почему asks what explains something
Use почему́ (pochemú, stress on the last syllable) when you want a reason or an explanation. It works for things people decide to do, things they forget to do, and things that simply happen.
Почему поезд остановился? — Why did the train stop?
Почему здесь так холодно? — Why is it so cold in here?
Почему ты не ответила? — Why didn’t you reply?
A useful answer starter is потому что (potomú chto), “because.”
Почему ты не ответила? — Why didn’t you reply?
Потому что не видела сообщения. — Because I didn’t see the message.
Sometimes the whole explanation is two words. Почему ты смеёшься? — Смешно же. “Why are you laughing?” “Because it’s funny!” In conversation, people give the reason in whatever form comes naturally. Потому что is a reliable way to start when you’re learning. Reference on cause and purpose in Russian
Зачем asks what something is for
Use заче́м (zachém, also stressed on the last syllable) when you want to know the purpose of an action or what use something has.
Зачем ты идёшь в аптеку? — What are you going to the pharmacy for?
За пластырем. — To get an adhesive bandage.
Зачем вы открыли окно? — What did you open the window for?
Чтобы проветрить комнату. — To air out the room.
Чтобы (chtóby) introduces a goal. In a short answer like Чтобы проветрить комнату, it’s followed by an infinitive and the whole phrase translates naturally as “to air out the room.” With Чтобы дети не проснулись (“so the children wouldn’t wake up”), the children are the subject of the clause after чтобы. More examples of purpose clauses
Notice that зачем can ask about a goal even when nobody is named. Зачем здесь зеркало? (“What’s this mirror here for?”) makes sense because someone presumably put it there for a reason. Зачем здесь так холодно? sounds as though you suspect someone is deliberately keeping the room cold and want to know what they hope to achieve. If you’re simply wondering why the room is cold, Почему здесь так холодно? is the natural choice.
The same decision can have a reason and a purpose
Imagine asking someone about a trip to Kazan.
Почему вы поехали в Казань? — Why did you go to Kazan?
Потому что друзья нас пригласили. — Because some friends invited us.
Зачем вы поехали в Казань? — What did you go to Kazan for?
Чтобы увидеться с друзьями. — To see our friends.
The invitation and the visit belong to the same story. The invitation explains how the trip came about. Seeing friends was what the travelers wanted to do there. In real conversation, a person might mention both in a single answer. The question simply tells them which part you’re interested in.
That’s also why thinking of почему as “past” and зачем as “future” gets confusing. Both Kazan questions are in the past. The goal of seeing friends was in the travelers’ minds when they set off, and it’s still the goal when they tell the story afterward.
When “what for?” starts to sound like “what’s the point?”
Picture two people in a shop. One reaches for a bag of coffee, and the other asks Зачем ты покупаешь кофе? On its own, that could be a practical question. Add У нас дома две пачки (“We’ve got two bags at home”), and the point of the question changes. The speaker is asking whether buying more makes sense.
English can do the same thing. “What are you buying coffee for?” can be genuine curiosity or a mild objection, depending on when and how you say it. In Russian, зачем lends itself to that second reading because it puts the usefulness of the action up for discussion. Зачем спорить? can sound like “What’s the point of arguing?” or, in a gentler moment, “Why get into an argument over it?”
Почему can carry a reproach of its own. Почему ты мне не сказал? (“Why didn’t you tell me?”) can express hurt or surprise. The situation and the speaker’s tone matter with either word.
A useful phrase when you want a practical answer
Say someone at a hotel asks you to sign a form. Зачем вам моя подпись? (“What do you need my signature for?”) is a legitimate question. If your aim is simply to find out what the signature is used for, try Подскажите, пожалуйста, для чего нужна моя подпись? (“Could you tell me what my signature is needed for?”)
Для чего means “what for” and comes in handy for equipment, forms, and unfamiliar objects. Для чего эта кнопка? is a straightforward way to ask what a button does. Подскажите, пожалуйста is a useful opener when you’re asking a stranger or staff member for help.
Try choosing the answer first
When an English “why” could go either way, start by imagining the answer you hope to hear. Suppose a friend leaves a party early. You might expect Потому что я устала (“Because I was tired”) or Чтобы успеть на последний автобус(“To catch the last bus”). The first fits Почему ты так рано ушла? The second can answer Зачем ты так рано ушла?if you already have some reason to think she left early to get something done. If all you know is that she left, почемуgives her more room to tell you what happened. She may volunteer the bus story anyway.
That little bit of judgment is part of getting comfortable in conversation. It helps to say both versions aloud with another person and hear what each one invites them to tell you. Polyglottist Language Academy offers live Russian classes for adults online and in selected in-person groups in Berkeley, California. Learners get time to try everyday exchanges like these and hear how they sound in conversation. Explore Russian classes.