Subjunctive Mood

Introduction -- THE CATEGORY OF MOOD
The meaning of this category is the attitude of the speaker, or writer towards the content of the sentence. It is expressed
in the form of the verb.
There are three moods in English-the indicative mood, the imperative mood and the subjunctive mood.
The indicative mood indicates that what is said must be regarded as a fact, as something which has occurred or is occurring at the moment of speaking or will occur in the future. It may denote actions with different time-reference and different aspective characteristics. Therefore the indicative mood has a wide variety of tense and aspect forms in the active and passive voice.
The imperative mood expresses a command or a request to perform an action addressed to somebody, but not the action itself. As it does not actually denote a specific action it has no tense category; the action always refers to the future. Aspect distinctions and voice distinctions are not characteristic of the imperative mood, although forms such as, be writing, be warned sometimes occur.
The imperative mood form coincides with the plain stem of the verb, for example: Come here! Sit down. The negative form is built by means of the auxiliary do.
Do not take it away. Don't worry about the child. Don't be a fool.
Note: Do is also used in commands or requests to make them more emphatic: Do come and stay with us. Do be quiet.
In commands and requests addressed to a third person or persons the analytical form let... + infinitive is used. When the person addressed is denoted by a personal pronoun, it is used in the objective case. Let us go together. Let him finish his dinner first. Let Andrew do it himself.
In negative sentences the analytical forms take the particle not without an auxiliary. Let us not argue on the matter. Let him not overestimate his chances. Let her not go any further.
Note: In sentences like Don't let him go the negation refers to the verb let, which in this case fully retains its original meaning of permission.
The analytical forms differ in meaning from the synthetic forms, because their meaning is closely connected with the meaning of the pronoun included in the form. Thus let us do smth denotes an invitation or a joint action, not an order or a request. Let him do it retains to some extent the meaning of permission.
Note: In the form let me (let me do it) the first person singular does not convey By imperative meaning and should not therefore be regarded as the imperative. It conveys the meaning of I am eager to do it, allow me to do it.
The imperative mood is used only in imperative sentences and can't be used in questions

THE SUBJUNCTIVE MOOD
The Subjunctive Mood shows that the action or state expressed by the verb is presented as a non-fact, as something imaginary or desired. The Subjunctive Mood is also used to express an emotional attitude of the speaker to real facts. In Modem English the Subjunctive Mood has synthetic and analytical forms. "I wish I were ten years older," I said. (Braine) “Хотел бы я быть на десять лет старше”, — сказал я. I wish you would speak rationally. (E. Bronte) Я хотел бы, чтобы вы говорили разумно.
The synthetic forms of the Subjunctive Mood can be traced to the Old English period, when the Subjunctive Mood was chiefly expressed by synthetic forms. In Old English the Subjunctive Mood had a special set of inflections, different from those of the Indicative.
In course of time most of the inflections were lost and the difference between the forms of the Subjunctive and those of the Indicative has almost disappeared. However, in Modern English mere are a few synthetic forms of the Subjunctive which have survived; they are as follows: the Present Subjunctive of all the verbs and the Past Subjunctive only of the verb to be.
I. The Present Subjunctive. In the Present Subjunctive the verb to be has the form be for all the persons singular and plural, which differs from the corresponding forms of the Indicative Mood (the Present Indefinite). In all other verbs the forms of the Present Subjunctive differ from the corresponding forms of the Indicative Mood only in the third person singular, which in the Present Subjunctive has no ending -s.

…