“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 and there at the start of a sentence, it will instead warn of something still to come (see 145. Highlighting with “What” Sentences and 161. Special Uses of “There” 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 ineffective.
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 are often best 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 partly because it is inappropriate, but also 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 situation where they do, 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). Placing an -ing verb at the start of a sentence instead of at the end after an introductory it could well be another such structure.
Thus, if in (b) visiting museums is familiar information (the focus of the sentence being on rewarding), then these words ought to come first instead of it. However, if visiting museums is the focus of the sentence 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 seems quite widely possible to use that between a starting it phrase and a subsequent verb. Sometimes that is the only possibility, and sometimes other possibilities are more common. That seems to be the only possibility after It is and a truth-commenting adjective (or noun) like certain, definite, a fact, false, incorrect etc. (for a fuller list, see 153. Conjunction Uses of “that”). An example is:
(e) It is TRUE (THE TRUTH) that social benefits can end poverty.
Such sentences are a common way of expressing agreement or disagreement (see 152. Agreeing and Disagreeing in Formal Contexts). Note that expressions of doubt rather than falsehood, such as debatable, doubtful, not clear, uncertain and questionable, are more likely to have whether than that.
Another group of that-requiring expressions is adjectives made by adding -able to a verb of saying or thinking. Examples are arguable, foreseeable, notable, observable, predictable, tenable and understandable.
In some other it sentences a need for that seems to depend mainly on the way the second verb is being used. Compare the following:
(c) It is not surprising that antibiotics are becoming ineffective.
(g) It is surprising seeing so much flu in summer.
In (c), are becoming has the visible subject antibiotics, but in (g) seeing has no visible subject. Visible subjects are what make that necessary after surprising. But what makes visible subjects necessary? In general, it is when the meaning is not I or you or people. The subject of are becoming is obviously none of these; whereas the unspoken subject of seeing is I, the speaker of the sentence.
Here is a sentence without that which has the invisible subject people:
(h) Is it acceptable to buy alcohol in supermarkets?
If alcohol is made the subject of a verb here (…alcohol is on sale in supermarkets?), that becomes necessary.
The kind of adjectives that are illustrated by surprising and acceptable mostly seem to express the causing of particular emotions like surprise and acceptance. Other examples are annoying, awful, delightful, depressing, heartening, irritating, painful, pleasing, regrettable, saddening, satisfying, shocking and terrible.
2. Verbs with “to” or “-ing”
When that cannot be used in an it sentence, there are some rules for choosing between to and -ing. We have to choose to if there is an adjective at the start that generally in English combines with to verbs rather than -ing ones, such as important in (a) above. Here is a list of common adjectives like this:
Common Adjectives that Require a Later “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
Of particular interest within this list is possible. For details of its use with that (+ visible subject) and to (with no visible subject), see 181. Expressing Possibility.
In contrast to the above adjectives, those that elsewhere can be followed by either to or -ing allow the same choice in it sentences, but with different meanings. This is the case, for example, with rewarding in (b) above. Here is a list of common adjectives of this kind:
Common Adjectives that Allow a Later Choice between “to” & “-ing”
amusing, difficult, easy, enjoyable, funny, good, hard, hurtful, impressive, nice, normal (= “right”), painful, pleasant, rewarding, safe, satisfying, strange, surprising, thrilling, tricky, useless
Some of these – easy, enjoyable, safe, useless, for example – cannot be used with that. If a subsequent verb needs a visible subject, a for…to… structure must be used (It is easy for children to…).
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. Noun Countability Clues 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.