In my Russian course we have learnt that in negative sentences the object is often in the genitive. On the other hand there are situations in which it is correct to use an accusative, and there is also a difference in meaning.
Here are some examples (the first is from my textbook):
- Не люблю я зтой химии = I do not like (this) Chemistry (said by a student).
- Не хочу воды / хлеба = I do not want (any) water / bread.
- Не хочу воду = I do not want the water (this concrete water in the bottle on the table).
So, as far as I understand, you often use the genitive to express the object of a negative sentence, and I have a vague intuition that the accusative has a more specific, concrete meaning.
However, when speaking, I am always in doubt whether I should use the genitive or accusative and whether this will change the meaning of my sentence. Is there some general rule? What different meanings are expresses with the genitive resp. accusative?