除非

1. (used correlatively with 才) only if; only when

♦ ~他做不了, 他才会找我帮忙。 Only when he can't do it does he ask me for help.

2. (usu. used correlatively with 否则, 不然, or 要不然) (not) ... unless

♦ ~你跟我去, 否则我不去。 I won't go unless you go with me.

3. (preceded by a clause with 要) must needs; necessarily

♦ 要想取得第一手资料, ~你亲自去作调查。 If you want firsthand information, you'll have to find out for yourself.