Subjunctive Mood

Present Subjunctive
This form is always identical to the infinitive. This means that apart from the verb to be, it is distinct from the indicative present only in the third person singular and the obsolete second person singular.
It is used to express wishes about the present or future:

God save our queen. (Not: God saves our queen, which means that it actually happens)

It can be used (in formal writing) to express present doubt, especially after if, whether, and lest and in set phrases:

If that have any validity....

If that be true,....

If he need go,....

If music be the food of life,....

Whether that be true or not,....

Lest he arrive too soon,....

Be that as it may,....

The subordinate conjunction whether can be replaced by inversion of be and the subject:

Be that true or not,....

It is also used in a mandative sense:

He insists that his son have a more conventional celebration. (He strongly wants that to be true in the future; contrast with the indicative usage He insists that his son has a more conventional celebration, in which he asserts that it is a fact.)

It is important that the process be carried out accurately.

I shall work for him on condition that he pay me weekly.

The present subjunctive can be written in the passive voice as in

If it be written,....

Imperfect subjunctive

The imperfect subjunctive is used to express hypotheses about the present or future: it is used to describe unreal or hypothetical conditions. It consists of the verb were in all persons and numbers (including the first and third persons singular), either as the main verb or as a helping verb combined with the infinitive of the main verb.
It usually appears in "if clauses" of conditional sentences. Examples include:

• If I were rich, I would retire to the South of France.
• If I were a boy,....

Especially in formal usage, if may be omitted and the order of the subject and were inverted:

• Were I to speak, I would do so softly. (This is identical in meaning to If I were to speak,....)

When if means when (a fact) then the indicative is used. Compare

• If I were walking down the road, I would greet him. (The subjunctive is used for a hypothetical present situation; the main clause is in the conditional.)
• If I was walking down the road, I would greet him. (The indicative is used for a fact about habitual actions in the past; the main clause is in the past time and habitual aspect.)

The imperfect subjunctive is also used in "that clauses" after a wish:

• I'd rather that it were more substantial.
• I wish she were here.

This last example can be contrasted with I want her to be here, in which the indicative rather than the subjunctive is used because there is a substantial possibility that the hypothesis is (or will be) true.
The imperfect subjunctive can be written in the passive voice as in

If it were written....

or

Were it written....

Future subjunctive

A future subjunctive for use in "if clauses" can be constructed using the conjugated form of the verb "to be" plus the infinitive (including the particle to) or by using the modal auxiliary verb "should" (though the should form is very unusual in American English):

If I were to die tomorrow, then you would inherit everything.

If I should go, then will / would you feed the hens?

These constructions can alternatively be expressed with inversion of the order of were or should and the subject, with if omitted:

Were I to die tomorrow, then you would inherit everything.

Should I go, then will / would you feed the hens?

If the were to constructions is used in the "if clause", the word would is used in the main clause; if the shouldif clause", either will or would can be used in the main clause, depending on whether the event is very hypothetical (leading to the use of would) or is quite possible (permitting the use of will). form is used in the "
The passive voice can be applied to the future subjunctive as in any of the following:

If it were to be written tomorrow,....

Were it to be written tomorrow,....

If it should be written tomorrow,....