A practical english grammar - Vyssaja skola 1978
Structures that take the place of nouns
Sound symbols
The subject of a sentence is usually a noun or pronoun, along with any modifiers it may have.
The room is cold.
He left.
A long black car with foreign license plates entered the drive.
Verbal nouns. Sometimes the subject of a verb is a verb form functioning as a noun. That is, it may consist of a “nonfinite” verb (one that can not stand independently as the predicate of a sentence), along with any modifiers, objects, or complements it may have.
Writing letters takes all my free time.
To answer all these questions is not easy.
The sentences just given show, first, a gerund (an ing-form used as a noun) and, second, an infinitive (to + base form). Notice that, although the nonfinite verbs writing and answer act as nouns, they retain their verb-like character to the extent of having objects (letters, questions).
Noun clauses. A clause is a structure with a subject’ and a verb and is just like an ordinary sentence, except that it can not stand alone as an independent sentence, because of its place in a larger sentence, the presence of special introductory words, or some other reason. Clauses introduced by that often function as nouns.
That he was not in the house is fairly certain.
Use of the dummy subject IT. There is a tendency in English to put heavy elements at the end of the sentence. An element with several words in it is “heavy” in this sense. Thus, if the subject of a sentence is a verbal noun, with complements or modifiers, or a clause consisting of half a dozen words or more, a way is needed to get this element at the end of the sentence instead of the beginning, where the subject normally occurs. (Almost all infinitive subjects are handled this way, whether they have complements and modifiers or not.) This is done by temporarily replacing the subject with the dummy word it and putting the real subject after the predicate.
It isn’t easy to answer all these questions.
It’s interesting to watch a bird build a nest.
It’s fairly certain that he was in the house.
It’s possible that the price will go down.
This pattern is not quite as frequent with gerunds as it is with infinitives and clauses, but it sometimes occurs.
It’s fun writing letters here on the terrace.