There is a fuzzy border between tidak and bukan. For example, what do you say if you want to answer “no” to this question?
Apakah mobil Anda mobil baru?
Is your car new?
If the emphasis in the question is mobil Anda, or mobil baru (both noun phrases) then the appropriate answer is Bukan. But if the emphasis in the question is baru (an adjective) the appropriate answer is Tidak.
Also, when you want to negate certain prepositions (words like di, di depan, di belakang etc.) bukan seems to be used as much as tidak. Take, example, this exchange:
Di sini? Di belakang?
Here? At the back?
Bukan! Di sana!
No! Over there!
As this example suggests, bukan is more emphatic, or “stronger”, than tidak. This is especially evident when you want to emphasise a contrast or distinction. Supposing you want to stress that you definitely don’t live in Medan, you live in Padang. You might say something like this.
Saya bukan tinggal di Medan… Saya tinggal di Padang.
I (definitely) don’t live in Medan…I live in Padang.
Tinggal is a verb, so normally tinggal would be negated with tidak. But in this sentence it is negated with bukan because bukan is more emphatic and the speaker wants to stress that he/she doesn’t live in Medan.
You don’t need to worry a lot about these nuances and variations – you will get a sensitive feel for them as your command of Indonesian deepens. For the moment concentrate on negating nouns with bukan, and negating all other parts of speech with tidak. Tidak is used to negate verbs, adjectives and prepositions.
