Shall and will are both modal verbs primarily used to express the future tense.

Shall currently tends to be falling out of use, but it continues to be used 
with I and we for offers and suggestions.

  • Shall I open the window?
  • Shall we dance?

Should is the conditional form of shall 

Would is the conditional form of will.


Will have or would have?

- We use the perfective will have when we are looking back from a point in time when something will have happened. 

Ex: I will phone at six o’clock. He will have got home by then.


- or looking "back" from the present:

Ex: Look at the time. The match will have started.


- We use would have as the past tense form of will have:

Ex: I phoned at six o’clock. I knew he would have got home by then.


- We use would have in past conditionals to talk about something that did not happen:

Ex: He would have been very angry if he had seen you.

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