Subjunctive

The subjunctive is a special kind of present tense, using an infinitive that has no –s in the third person singular.  It is often used when talking about something that somebody must do.

            I insist (that) your friend leave this house at once.   

The subjunctive is a formal construction.  It is more commonly used in American English than in British English, and more often in the written form than in the spoken form.  It was used much more frequently in old English, but many of these forms have now disappeared in modern English.

That-clause

It is often used with a that-clause, especially in American English, to formally express the idea that something is important or essential. 

            I demand that he leave at once.

Verbs used with the Subjunctive

Other verbs that are commonly used with the subjunctive are: advise, ask, beg, decide, decree, desire, dictate, insist, intend, move, order, petition, propose, recommend, request, require, resolve, suggest, urge, and vote.

            Tom suggested that his friends stay over for the night.

            Sam proposed that Tom telephone his accountant.

            She recommended that he go and see a doctor.

            The manager requested that everyone put their requests in writing.

            He insisted that she stay until the end of the week.

            The Queen commands that he attend the ceremony.

            He urged that a business manager be hired to help things run more smoothly.

            I simply requested, politely, that she refrain from smoking in my house.

            Sam recommended that you join the committee.

            The professor asked that Tim submit his research paper before the end of the week.

The verb ‘be’

‘Be’ has special subjunctive forms: I be, you be, she be, they be, etc.

            It is vital that you be truthful about what happened.

            He suggested that she be more vocal in the next meeting.

            She urged that the matter be resolved in a family court.

            Hadrian decreed that a new temple be built in the honour of Jupiter.

Adjectives used with the Subjunctive

Some adjectives can be followed by a subjunctive verb, like anxious, determined, eager.

            He was determined that they not separate.

            The political campaign is eager that their candidate step out of the shadows.

            I am anxious that he discuss this with me soon.

Certain adjectives can also be used with the subjunctive and `It`, like advisable, critical, desirable, essential, fitting, imperative, important, necessary, vital.

            It is imperative that you get home before dark.

            It is important that everyone follow the rules.

            It is necessary that everyone be calm in times of danger.

            It is essential that you arrive before 5pm.

            It is critical that the prime minister address those sensitive issues.

            It was vital that everything be done on time.

            It is crucial that we make it successful.

Nouns used with the Subjunctive

There are also nouns that can be followed by a subjunctive verb, like advice, condition, demand, directive, intention, order, proposal, recommendation, request, suggestion, wish.

            My advice is that the company invest in new equipment.

            She is free to leave, on condition that she commit no further offence.

            His deep wish is that his daughter go to university.

Less Formal Usage

There are several alternatives to the very formal standard subjunctive:

·        Should 

This construction is more common than the subjunctive in British English: 

            Tom suggested that his friends should stay overnight.

            She recommended that he should go and see his doctor. 

·        The Indicative 

This construction is also used sometimes in British English, but is rare in American English: 

She has demanded that the machinery undergoes vigorous tests to ensure high quality.

It is imperative that more decisions are made by the shareholders. 

·        For + Infinitive 

It is essential for everyone to be informed of the new regulations. 

·        No Tense Change 

In colloquial English, it is possible to not make a tense change:

             She demanded that he left.

            She felt that it was necessary that she wrote a thank you letter to them. 

Fixed Expressions using the Subjunctive

…, as it were	(in a way, so to speak)
Be that is it may...	(Whether that is true or not…)
Come what may…	(Whatever happens…)
Far be it from me to disagree/criticise	(To appear less hostile when disagreeing)
God bless you.
God save the Queen!
Heaven help us!	(An exclamation of despair)
Heaven forbid!	(An exclamation that you hope something won’t happen)
If need be...	(If it is necessary)
Long live the bride and groom!
…, so be it.	(We can’t do anything to change it)
Perish the thought!	(A suggestion or possibility is unpleasant or ridiculous)
Suffice it to say…	(It is obvious/I will give a short explanation)

                                      

Were-Subjunctive

In hypothetical sentences, were is usually used instead of was:

                        If I were you, I’d learn how to drive.

                        I wish it were Friday.

It is important to note that was can also be used (although still considered incorrect by some grammarians), and is, in fact, more common in informal English.

                        Sometimes I wish I was/were taller.

Source: http://www3.telus.net/linguisticsissues/subjunctive.html