These two moods will be treated together because they have the same meaning and are practically interchangeable in use. They differ in form as well as stylistically.
Forms: Subjunctive I is a synthetical form surviving from Old English. It has only one form which is homonymous with the plain verb stem: be, do, have, go, write, etc. The negative form of Subjunctive I is not be, not do, not have.
The Suppositional Mood is an analytical form built up with the help of the auxiliary verb should for all persons plus the infinitive. The non-perfect Suppositional Mood: should be, should do, should write. The perfect Suppositional Mood: should have been, should have done, should have written.
Meaning: Both Subjunctive I and the Suppositional Mood express problematic actions, not necessarily contradicting reality. These actions are presented as necessity, order, suggestion, supposition, desire, request, etc.
Expressing the same kind of modality, Subjunctive I and the Suppositional Mood are used in the same syntactic structures and are, to a great extent, interchangeable. However, they differ stylistically: thus, in the British variant of the English language Subjunctive I is rapidly falling into disuse and is only preserved in elevated prose, poetry or official documents. In neutral, everyday speech the Suppositional Mood is used. In American English Subjunctive I in neutral and colloquial speech is the norm:
Cf: He even suggested that I should play cricket with his sons. (Br. E.) He suggested that I come for her. (Am.E.)
Use: The Suppositional Mood and Subjunctive I are used in simple sentences and in certain subordinate clauses of a complex sentence.
In simple sentences only Subjunctive I is used in a few set expressions as a survival of old usage (the so-called formulaic expressions).
1. Most of them express a wish:
Long live the Army / patriotism / heroes, etc.! Glory be! Success attend you!
Be yours a happy meeting! Far be it from me to spoil the fun / to argue with you / to
conceal the truth. God bless you! God save the Queen! Heaven forbid!The Devil take him! etc.
Subjunctive I in such expressions can be replaced by may + infinitive:
May success attend you! May your meeting be happy! May the Army live .long!
2. Some formulaic expressions have a concessive meaning:
Happen (come) what may (will) / Cost what it may.
So be it/ Be it so / Be that as it may. Be it rain or snow / Come rain or shine. Subjunctive I in these expressions may be replaced by let + infinitive: Let it be so.
3. The only productive pattern of a simple sentence with
Subjunctive I is the sentence expressing a command or a request
with an indefinite pronoun as the subject:
Everybody leave the room! —Somebody switch off the light! —
Subjunctive I may be replaced in such sentences by let +infinitive: Let everybody leave the room.
4. The Suppositional Mood is used only in one type of interrogative sentences beginning with 'And what if ... ?'
And what if he should come back?
Subjunctive I and the Suppositional Mood are used in nominal (subject, object, predicative), attributive appositive and some adverbial subordinate clauses.
NOMINAL AND ATTRIBUTIVE APPOSITIVE CLAUSES
1. Both Subjunctive I and the Suppositional Mood (non-
perfect) can be used in subject, object, predicative and
attributive appositive clauses if in the principal clause a modal
meaning is expressed (one of order, recommendation, suggestion, supposition, desire, command, etc.)
It is required that all (should) work hard, (object clause)
(attributive appositive clause) ''■It is important that a young man (should) have really
trustworthy friends. (subject clause) He suggested that I (should) go out and help them, (object
clause) , I haven't the least desire that you should dine with me on
that day. (attributive appositive clause)
My greatest wish in the world is that you should be happy.
2. Only the Suppositional Mood (both non-perfect and perfect) is used in nominal and attributive appositive clauses if in the principal clause a personal reaction to events is
expressed (for instance, with words like amazing, interesting, shocked, sorry, normal, natural, it's a shame, etc.): It was astounding that so short a break should have destroyed the habit of years, (subject clause) Tm surprised you should want him to stay in that house. (object clause)
A feeling of anger seized her that a letter from Gerald should bring her such pain, (attributive appositive clause)
3. The Suppositional Mood (mostly non-perfect, though perfect is also possible) and rarely Subjunctive I is used in nominal and attributive appositive clauses after the expression of fear in the principal clause. The subordinate clause may be introduced by the conjunction that or the negative conjunction lest (typical of a literary style):
I was terrified lest they should notice me. (object clause) I'm very much afraid that I shouldn't be acceptable, (object
clause) Our fear lest he should give away our secret was great.
(attributive appositive clause) Our fear was lest we should be late, (predicative clause)
1. In adverbial clauses of purpose introduced by the conjunctions so that, lest (literary' style) the non-perfect Suppositional Mood is used or, rarely, Subjunctive I: Mary lowered her eyes so that he should not see the faint dream of amusement in them.
2. In adverbial clauses of concession introduced by though, although, whatever, whoever, whenever, wherever, etc., the non-perfect Suppositional Mood or Subjunctive I may be used with
reference to the present or future: Though he should make every effort he cannot succeed.
More usual, however, are the modal phrases may (might) •f infinitive: Whoever he may be, he has no right to be rude. Though he might have been suspicious, he gave no sign.
3. In the adverbial clauses of condition referring to the future the Suppositional Mood is used to show that the action is possible, though unlikely. Such clauses may be rendered into Russian as ñëó÷èëîñü òàê, ÷òî…, åñëè ñëó÷àéíî;
In the principal clause the Conditional Mood, the Future Indicative or the Imperative Mood may be used:
If it should be wet they would stay at home. If you should find another way out, will you inform me?
In a literary style conditional clauses of this type are sometimes joined to the principal clause asyndetically, by means of inversion:
Should a conflict ever flare up in Europe, it would immediately blow up into a world war.
After the conjunctions that, so that, in order that, so the modal phrases may (might) or can (could) + infinitive may be used: