infinitives 2: forms

Besides the ordinary infinitive (e.g. (to) go, (to) work), there are also progressive, perfect and passive forms.
1 progressive infinitive: (to) be .. .ing
Like other progressive forms (see progressive 1: general), progressive infinitives suggest that actions and events are / were / will be continuing around the time that we are talking about.
It’s nice to be sitting here with you.
I noticed that he seemed to be smoking a lot.
This time tomorrow I’ll be lying on the beach.
(future progressive tense: see future 10: future progressive)
Why’s she so late? She can’t still be working.
2 perfect infinitive: (to) have + past participle
Perfect infinitives can have the same kind of meaning as perfect tenses (see perfect verb forms or past tenses see past 1: simple past I worked etc-422).
It’s nice to have finished work. (= It’s nice that I have finished.)
I’m sorry not to have come on Thursday. (= … that I didn’t come …)
We often use perfect infinitives to talk about ‘unreal’ past events: things that did not happen, or that may not have happened (see infinitives 10: I’m glad to have left).
I meant to have telephoned, but I forgot.
You should have told me you were coming.
I may have left my umbrella at the restaurant.
3 passive infinitive: (to) be + past participle
Passive infinitives have the same kind of meaning as other passive forms (see passives 1: passive structures and verb forms).
There’s a lot of work to be done. She ought to be told about it.
That window must be repaired before tonight.
Sometimes active and passive infinitives can have similar meanings, especially after a noun or be (see infinitives 9: active and passive infinitive with similar meaning).
There’s a lot of work to do / to be done.
4 combinations
Perfect progressive and perfect passive infinitives are common.
I’d like to have been sitting there when she walked in.
They were lucky – they could have been killed.
Progressive passive infinitives are possible but unusual.
What would you like to be doing right now? infinitives : formsI’d like to be being massaged. Progressive perfect passive infinitives (e.g. It must have been being built at the time) are very unusual.
5 negative forms
Negative infinitives are normally made by putting not before the infinitive. Try not to be late, (NOT USUALLY Try to not-be-late. OR Try to dowt be late.) You were silly not to have locked your car.
He’s very busy. I’m afraid he can’t be disturbed. ?
6 to
The marker to is normally used before infinitives (e.g. He wanted to go). Note that this to is not a preposition; after the preposition to we use -mg forms (see -ing forms 6: without breaking; before starting.2. For infinitives without to e.g. She let him go, see infinitives 3: without to.
7 split infinitive
A ‘split infinitive’ is a structure in which to is separated from the rest of the infinitive by an adverb.
I’d like to really understand philosophy.
He began to slowly get up off the floor.
Split infinitive structures are quite common in English, especially in an informal style. Some people consider them incorrect or careless, and avoid them if possible by putting the adverb in another position.
He began slowly to get up off the floor.
For details of the use of infinitives, see the following sections.
For the use of to instead of a whole infinitive (e.g. I’d like to), see ellipsis 6: infinitives.