What does '練習しなければ' mean on its own?

Question

I found the following sentence in a Japanese textbook:

"明日の試合に勝ちたいなら、きっと練習しなければ。 If you want to win tomorrow's game, you must practice."

This was in a section to do with なら, there was no explaination provided regarding the second half of the sentence. However the second half confuses me. Why does 練習しなければ mean 'must practice'?

I understand that 練習しなければ　is the negative conditional form of 練習する, which should mean "If I don't practice" or "unless I practice". Is this just an additional way to use this form (i.e. the negative conditional form for X can also mean 'must X')?　

Is this a shortening of 練習しなければならない? This makes sense to me, but I can't find any info online that suggests it's grammatically correct to shorten/contract '練習しなければならない' in this way.

Answer 1

You have answered your own question. It is indeed short for 練習しなければならない. It is quite clear from the context what the natural conclusion of 練習しなければ is, so there is no need to say it. The more you study Japanese the more of these unfinished sentences you will find.

The Japanese seem to have a proclivity for omitting unnecessary information in conversation, but this example is not that unusual even in English. If you said the sentence "If you don't practise" with rising intonation it would strongly suggest that "things won't go well" is the natural completion, i.e. you must practise.