The cleft sentence, so called because it divides a single clause into two separate sections, each with its own predicate, is a special construction which gives both thematic and focal emphasis to a particular part of the sentence.
According to the structure we distinguish 4 basic types of cleft sentences:
It is a good rest what you need most.
2) wh-cleft (pseudo cleft)
What you need most is a good rest.
3) reversed wh-cleft
A good rest is what you need most.
4) demonstrative th-cleft.
That’s what you need most of all.
From a clause such as John wore his best suit to the dance last night, it is possible to derive four cleft sentences, each highlighting a particular element of the clause.
It was John that/who wore his best suit to the dance last night. (Subject as focus)
It was his best suit (that) John wore to the dance last night.
(Direct object as focus)
It was last night (that) John wore his best suit to the dance.
(Adverbial modifier of time as focus)
It was to the dance that John wore his best suit last night.
(Adverbial modifier of place as focus)
Apart from the subject, direct object and adverbials the two less common clause elements the indirect object and the predicative can act as a focal element of a cleft clause.
It was John(that) he gave the book to. or It was to John (that) he gave the book.
It’s dark green that I’ve painted the kitchen.
The emphatic position may be occupied by a whole clause.
It was what she said that spoiled the impression.
Was it because dusk was gathering that you failed to see anything?
Appended clauses (повторы с уточнением)
There are several varieties of appended clauses, modelled on the pattern of the main clause. These are used to intensify or reinforce a statement in the previous clause. The most common type of appended clauses are disjunctive (tag) questions. You are tired, aren't you? You are not ill, are you?
In non-formal style there is another form of appended clause, which is elliptical.
He is always very gloomy, is that John of yours.
She is a clever girl, is your friend.
In such sentences the link-verb to be is generally repeated, or a form of the verb to do is used.
He never told me anything, did your brother.
Absolute (or independent) subordinate clauses
Subordinate clauses may be used absolutely as independent exclamatory sentences. They may have the form of a conditional or comparative clause.
If only I knew his address!
As though you didn’t know!
That he should be so late!