Is 'need to' a modal auxiliary?

need to並不是助動詞(a modal auxiliary)
need其實也可以作助動詞時，但它助動詞時通常用於否定句或疑問句，並助如may, can等等的助動詞，後面直接跟著動詞便可，並不用to infinitive(to不定詞)。而作助動詞的need，即使主詞為第三人稱單數現在時式，也不可加-s，並且否定形和疑問形也不用do，此外，它後面不接名詞及代名詞，而本身也沒有過去形。
如：He need not come.(他不必來）
I need hardly say that I like you very much.（不用說，我當然非常喜歡你）
請你留意以下兩句的分別
You need not have done so.(你並不必這樣做）（need作助動詞）
You did not need to do so.（你不必這樣做）（need 作主動詞）

2007-04-28 10:16:54 補充：
其實你不應將need to連在一起，這句應這樣分：We(subject) need(main verb) [to work] (to infinitive) hard (adverb)

'need to' is not a modal auxilliary, it's just used as an ordinary verb here, simply because 'need' is usually followed by the 'infinitive' with 'to'
ie Everyone needs to rest sometimes

Modal auxiliary form:
--> 'need' will followed by an 'infinitve' without 'to'
ie You need not fill in a form.
in this sense, the modal 'need' refers to immediate necessity and give permission but not general necessity or habitual

2007-04-28 12:53:02 補充：
epistemic modal refers to a possibility or estimates likelihood of a fact or eventie He must be on his way to school. fromThe Cambridge Guide to English Usage by Pam Peters