Optative or auxiliary verbs are those placed before other verbs to express intention, wishes, possibility etc.
To express /subjective wish/, /desire/ or /request/:
要 + verb = to want to
我要喝橘子水。
想 + verb = would like to
你想看電影嗎﹖
To express /objective necessity/:
要 + verb = to have to (especially in questions)
我明天要來嗎﹖
Do I have to come tomorrow?
我們要去了。
We have to go.
不用 + verb = don't have to
你明天不用來。
You don't have to come tomorrow.
To express /ability/ or /skill acquired/:
能 + verb = can, be able to
你現在能看中文報紙嗎﹖
可以 + verb = can, be able to
你們一個星期可以學幾課﹖
會 + verb = can, be able to
他們都會游泳嗎﹖
To express /ability depending on circumstances/:
能 + verb = can, be able to
你明天能來嗎﹖
可以 + verb = can, be able to
你今天晚上可以1給他打電話嗎﹖
Note, in both cases use 不能 for negative sentences.
To express /permission/:
能 + verb = may, be permitted to
我能在這兒停車嗎﹖
你不能 (or 不可以) 在這兒停車。
可以 + verb = may, be permitted to
我可以在這兒吸煙嗎﹖
你不可以 (or 不能) 在這兒吸煙。
To express /possibility/ or /probability/:
. 會 + verb = be likely to, will probably
你明天會再來嗎﹖
今天晚上不會下雨。
To express /need arising from moral or factual necessity/:
應該 + verb = should, ought to
你們學得不錯﹐應該去中國。
他們不應該翻譯那本書。
Note:
To make a negation, put the negative word 不 or 沒有 before the optative verb:
他們不想給圖書館打電話。
To form an affirmative-negative question, alternate the optative verb instead of the main verb in the sentence:
你會不會唱中國民歌﹖
but not 你會唱不唱中國民歌﹖
It is possible to use more than one optative verb in a sentence:
你是北京人﹐應該會唱京劇。