Почему? Зачем? Отчего?
I have just completed the unit ‘Questions’ and I want to share some of my thoughts regarding the three ways to ask ‘Why?’ in Russian.
First of all, we have the work ‘Почему?’. As of my understanding, this ‘why’ asks for the cause of an action (or event), this cause maybe traced to the past. For example: ‘Why did she start cooking?/What made her start cooking?’ - ‘He started cooking because he became hungry.’
Then we have ‘Зачем?’. ‘Зачем’ asks for the purpose or the intention of an action or even, the thought behind it. For example: ‘Why is she cooking?/For what purpose is she cooking food?’ - ‘She is cooking food so that she can eat and stop being hungry.’
As we learn from the ‘Tips and notes’ for the unit ‘Questions’, some regions in Russia and the former Soviet Union does not differentiate between ‘Зачем?’ and ‘Почему?’ due to influence from other languages, e.g. Tatar in Tatarstan.
Lastly we have ‘Отчего?’. I am a little bit uncertain regarding this but I think that this question word asks for the cause (of an action or event) that does not include an active decision made by humans or that can be in the sense nature or mechanics. For example: ‘Why are the leaves green?/What makes the leaves green?’ - ‘They are green because they contain chlorophyll’; ‘Why does it rain?/What makes it rain?’ - ‘Rain is due to collections of water falling down from the clouds.’
Please, feel free to correct me if I’m wrong.
Also, I would recommend a series of children’s books called ‘Зачем? Отчего? Почему?’ for reading simple Russian literature: http://goo.gl/kCS2Vp.