From what I understand «зачем» means "for what purpose", and trying to distinguish between that and «для чего» doesn't translate well. Additionally, how does «зачем» compare with «почему»?
Зачем refers to factual purpose, while для чего is for intended purpose (для чего эта кнопка? "what is this button for?" vs. зачем ты нажал эту кнопку? "why did you press this button?").
Почему asks for reasons or causes, not purposes, i.e. where meaningful intent is not involved (generally, anyway; you might come across some examples that blur these distinctions).
5in both your examples зачем and для чего are interchangeable, I believe.– Quassnoi ♦Jan 21, 2016 at 18:56
1"Для чего ты нажал эту кнопку" is the same as "зачем ты нажал эту кнопку". There is no difference. Same for "для чего эта кнопка".– AbakanJan 22, 2016 at 9:04
@Quassnoi I've given it some more thought (judging by the comments, I'm ready to believe this time I've really made a contentious proposition) and I think that they are interchangeable, but asymmetrically so. Для чего can much more often be replaced by зачем than vice versa. For instance, if the pressing of the button was a pointless/annoying/disastrous thing to do, it's a very зачем situation; and that's consistent with the idea that для чего is asking about intentions which are, in this case, barely relevant. Jan 23, 2016 at 3:49
Both «зачем» and «для чего» in questions are synonyms and have the meaning "for what purpose?".
In contrast, «почему» means "for what reason?" (or "what is the reason?").
Для чего = What for
Почему = Why
Зачем may mean either of the two, though the latter belongs mostly to XIX century speech:
Зачем у вас я на примете?
Не потому ль, что в высшем свете
Теперь являться я должна;
Что я богата и знатна...
Зачем is about a purpose and почему is about circumstances.
Imagine you run into a friend in a shop and ask him why he's there. You could have the following dialogue:
- Зачем ты здесь? / Why are you here? - Купить молока / To buy some milk
Or this one:
- Почему ты здесь? / Why are you here? - У меня кончилось молоко / I ran out of milk
The difference is subtle, and you can almost always replace one with the other without any problem.
So, let's start, guys and girls! Зачем means -what is your purpose, aim, cause. Почему-basing on what! Для чего-what you do mean/waiting, after thing you did/told etc. P.S.-you can text me, I will always help you with Russian language in a simply understanding form!