The semi-modal NEED

Present and future

Need can behave either as a modal verb or as a main verb:

• As a modal verb, need is most typically used in negative sentences or in affirmative sentences with a negative meaning. It expresses absence of obligation or necessity, and it is followed by a bare infinitive:
  

  You needn't worry about that.
  No one need be surprised at what happened.
  You need only just ask.
  I doubt whether I need help you.

  Need as a modal verb also occurs in interrogative sentences, but this use is much more formal:

  Need you make so much noise?

• Need as a main verb is followed by a to-infinitive and expresses that something is necessary. It can be used in affirmative, negative and interrogative sentences:
  

  Do you have a minute? I need to talk to you about something.
  I don't need to be told that I should lose weight.
  Do you need to use the hairdryer?
  If you want good results, you will need to work harder.

Past

• The past tense of the main verb need to is needed to:
  

  I needed to have my hair cut.
  Why did they need to change the lock?

  The negative form didn't need + to-infinitive normally refers to actions which were unnecessary and were not performed:

  We didn't need to buy any milk. We had plenty at home. (we didn't have to buy any milk, and we didn't buy any)

• Need as a modal does not have a past tense form. Needn't + perfect bare infinitive (have + past participle), however, is used for actions which were performed but were unnecessary:
  

  We needn't have bought any milk. We still have plenty at home. (we bought some milk, but it wasn't necessary)