COMMAND:
I.Commands expressed by the imperative
A.The second person imperative:
1.This has the same as infinitive without to:
->Hurry!
->Wait!
->Stop!
->Listen!
For the negative we put do not ( don’t) before the Verb:
->Don’t hurry!
->Don’t cry!
->Don’t talk!
=>2 The person  addressed is very often not mentioned,    but can be expressed by a noun  placed at the end of phrase:
-> Eat your dinner, boys!
-> Be quiet, Tom!
These nouns can be placed before the verbs, this    is much less usual.The pronoun you is rarely used unless the speaker wishes to be rude, or wishes to make a distinction, as in:
->You go on; I’ll wait.
3.Do can be placed before the affirmative imperative:
->Do hurry.
->Do be quiet
this do could be persuasive, but could also express irritation.
=>>B. The first person imperative
Form: Let us ( let’s ) + infinitive  without to
->Let’s wait for Bill.
->Let’s do this exercise.
for the negative we normally put Not before the infinitive:
->Let’s not tell anyone.
By Let’s  the speaker can urge his hearers to act
in a certain way, or express a decision which         they are expected to accept or express a suggestion.
Shall we? is sometimes added to suggestions.
Approval of suggestions can be expressed by        Yes, let’s In indirect speech let’s is usually treated as a suggestion.
=>C. The third person imperative            Form : let him/ her / it / them + infinitive to:
->Let them  go by train.
but this is not a very common construction in         modern English. It would be more usual to say:
1>. They must go by train.
2>. They had better go by train.
Similarly in negative :
1. They had better not  go by train.
2. They must not go by train.
The negative third person imperative : Let him,etc     not go is not  used in modern English.
=>II. Other Ways of  Expressing Commads A. Subject + shall for third person commands ( in written  English)
->Shall can be used in very formal written regulation which will normally remain in force for            some time. These are very often in passive:
->The chairman shall be elected annually.
->Thief shall be punished.
->The winner shall be given a reward.
=>B. Subject + will mainly for third person commands.
-> When  the alarm rings, passengers and crew will assemble at their boat stations. “Will” used in this way indicates that the person giving order is quite certain that he will be obeyed. It is chiefly in written instructions by people who have some authority, e.g. captain of ships, officers of services, headmasters of schools, trainers of sports teams , etc
=>C. Commands are often expressed as obligations by must.
->You must not smoke in the petrol store.
->Passengers must cross the line by footbridge.
->you must pay school fee.
=>D. Instructions or orders can be conveyed by the    be + infinitive
construction:
->You are to report for duty immediately.
->You are to do this assignment.
=>E. Prohibitions may be expressed  in written     instructions by may not.
Candidates  may not bring textbooks into the    examanition room.