“It” at the start of a sentence can stand for a later verb with “to” or “-ing” or “that”
HOW “it” CAN REPRESENT A FOLLOWING VERB
When it starts a sentence, it could just be representing an earlier noun (see 28. Pronoun Errors), but sometimes, like what at the start of a sentence, it will instead warn of something still to come (see 145. Highlighting with “What” Sentences). What it warns of is a verb near the end of the sentence, adapted to perform like a noun. We understand as a result that the adapted verb is the “real” subject of the sentence, and it is just its substitute. Here are some examples (adapted verbs underlined):
(a) It is important to observe any changes.
(b) It is always rewarding visiting museums.
(c) It is not surprising that antibiotics are becoming less effective.
As these show, the adapted verbs represented by it may have to (to observe) or -ing (visiting), or a conjunction use of that (that … are becoming – see 153. Conjunction Uses of “that“). An occasional alternative to that is a question word like whether or where (see 88. Exotic Grammar Structures 1, #8). We know that these noun phrases are the “real” subjects of the sentences because putting them at the start of the sentence instead of it would not change the basic meaning – even though the grammar, especially with the infinitive (To observe … is important), would often sound strange (see 100. What is a Grammar Error?).
Also notable in the above examples is the presence just after it of is and an adjective. These are not the only possibilities, but are used above partly because they are simple and partly because they are common in academic and professional writing. A wide range of verbs can be found after it (e.g. It makes sense to …), and if the verb is one that, like BE, needs a “complement”, the complement can be a noun as well as an adjective (e.g. it seems a shame that …), and can even be an adverb (cf. all very well in 159. Exotic Grammar Structures 2).
Two important questions are raised by the possibility of using it in the way above: when and when not to employ it, and which form to give to the verb represented by it.
GUIDELINES FOR PLACING A VERB AT THE END OF AN “it” SENTENCE
There is a simple enough basic guideline for using it in the described way: consider doing so when the subject of your sentence would otherwise be a verb with to or -ing or that. The reason is the principle of what grammarians call “end weight”: that long phrases in English ought to be positioned at the end of a sentence. Verbs adapted to act like a noun phrase are nearly always long.
An apparently different guideline that is sometimes given is the need to avoid an unwanted subject like I or we in formal writing. Such a reason is indeed mentioned within this blog in the posts 46. How to Avoid “I”, “We” and “You” and 107. The Language of Opinions. The former discusses sentences where the passive voice of the main verb is not desirable, such as the following:
(d) I enjoyed sampling the product.
Using it to avoid I, this can be rephrased It was enjoyable sampling … . However, this reason for using it is not really so different from the one described above. The use of the passive was enjoyed is ruled out not because it is impossible, but because it would result in a long phrase (sampling the product) being placed at the beginning rather than the end.
Yet despite all this, sometimes adapted verbs are not placed at the end of a sentence. Example (b), for instance, could quite easily begin Visiting museums … . What, then, could be a reason for using this alternative? I would suggest first of all that it should usually be considered only when the adapted verb has -ing or that since, as stated above, verbs with to rarely seem natural at the start of a sentence (for one common use, though, see 119. BE Before a “to” Verb). With -ing or that, the degree of familiarity to the reader of the idea in question may become more important than length for deciding its sentence position.
Familiar ideas – particularly recently-mentioned ones – are suggested elsewhere within this blog to go best at the beginning of sentences (see 37. Subordination: Grammar for Good Repetition and 156. Mentioning What the Reader Knows Already). English has various grammar structures that enable familiar information to be first, most notably the passive voice of verbs (through which writers can switch the positions of subjects and objects). Choosing not to represent some verbs with a preceding it could well be another such structure.
Thus, if in sentence (b) the idea of visiting museums is already familiar through an earlier mention, the primary message of the sentence being that it is rewarding, then these words ought to come first instead of it. However, if visiting museums does not express a familiar meaning – so that the sentence is introducing it as something rewarding – then this fact combined with the length factor makes the end of an it sentence strongly suitable.
THE FORM OF VERBS REPRESENTED BY AN EARLIER “it”
1. Verbs with “that”
It usually seems necessary to use that when the word(s) immediately after the starting it have the meaning of “true” or “false”, as in this example:
(e) It is true that social benefits can end poverty.
This kind of sentence often expresses agreement or disagreement with the statement after that (see 152. Agreeing and Disagreeing in a Formal Way). Other expressions like true include a fact, certain, clear, correct, obvious, right, undeniable, false, incorrect, unconvincing, untrue and difficult to accept.
Another group of that-requiring expressions have the meaning of “able to be said” or “able to be thought”. Examples are foreseeable, notable, observable, predictable, tenable and understandable. Note, however, that when a word of this kind throws doubt on the truth of the subsequent statement, whether may be preferred to that (e.g. debatable whether …).
In addition, that sometimes becomes necessary after an expression that in other it sentences would need a following to or -ing verb. This seems to happen when the verb has a particular kind of implied subject: any except “I” or “you” or “people”. In (a) above, for example, the implied subject of OBSERVE is “you” and to is used, while in (b) the implied subject of VISIT is “people” and -ing is used. In (c), on the other hand, where that is used, the subject of are becoming is not I or you or people but antibiotics.
The word surprising in (c) is easily shown to be usable with a following verb whose implied subject is “I” or “you” or “people”, so that that is not possible:
(g) It is surprising seeing/to see so much flu in summer.
The implied subject of SEE here is “I”. In the same way, in a sentence beginning Is it acceptable … , we can continue either … to buy alcohol in supermarkets? (implied subject of buy = “people”) or … that alcohol is available in supermarkets? For another situation where implied subjects determine a grammar choice, see 105. Questions with a “to” Verb.
2. Verbs with “to” or “-ing”
When that is not possible, the verb at the end of an it sentence takes its form sometimes from the word(s) next to it and sometimes from the meaning that the writer wishes to convey. The word(s) next to it become the main influence if they are of the particular kind that elsewhere require any verb straight after them to have to, such as important in (a) above. With such adjectives, the verb at the end of an it sentence also needs to. Here is a list of common ones:
Common Adjectives Usually Followed by “to” Rather than “-ing”
acceptable, advisable, allowed, appropriate, common, compulsory, critical, crucial, desirable, essential, important, necessary, normal (= “usual”), permissible, (im)possible, reasonable, recommended, unheard of, urgent, useful, usual, unusual, vital
The meaning that a writer wishes to convey becomes more important when the adjective after it is one typically followed by either to or -ing. This is the case, for example, with rewarding in sentence (b) above. Here is a list of common adjectives of this kind:
Common Adjectives Usually Followed by either “to” or “-ing”
amusing, difficult, easy, enjoyable, funny, good, hard, hurtful, impressive, nice, normal (= “right”), painful, pleasant, rewarding, safe, satisfying, strange, surprising, thrilling, tricky, useless
The choice between to and -ing seems to depend on how the action is viewed (what grammarians call “aspect”): to to view it overall from the outside and -ing to view it as it is being experienced. Thus rewarding to visit means that the reward is the complete act of visiting, while rewarding visiting means that the reward comes as the visiting proceeds.
There is a similarity here to the choice between to and -ing after the object of a perception verb like HEAR (… hear them go/going – see 148. Infinitive Verbs without “to”), and to the choice between -ing and an “action” noun for some kinds of sentence subject (see 131. Uses of “Action” Nouns).
A problem thrown up by the existence of the two different kinds of adjectives listed above is the difficulty of knowing and remembering which kind particular adjectives belong to. Is there any guideline? One that might exist is the kind of meaning that the adjective has. Kinds of meaning have quite often been suggested within this blog as a useful basis for identifying grammatical behaviour – see, for example, 14. Countable Noun Meanings 1, 83. Active Verbs with Non-Active Meanings (2), and 92. Complement-Showing “As”. Readers might like to look again at the two verb lists above to see what overall meaning each may reflect.
An overall meaning that stands out for me is that of personal feelings in the second list. To say it is enjoyable without also saying for me is nevertheless to suggest I enjoy. Using it with a word from the first list, by contrast, (e.g. it is acceptable …) seems to suggest not just my feeling but everyone’s.