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Infinitives: forms

Infinitives are most often used with to (e.g. to go, to start). For infinitives without to, (see here). Besides simple infinitives, there are also progressive infinitives (e.g. (to) be writing), perfect infinitives (e.g. (to) have written), and passive infinitives (e.g. (to) be written).

Progressive infinitive: (to) be …ing​

Like other progressive forms (see here), progressive infinitives suggest that situations 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 here)
  • Why’s she so late? She can’t still be working.

Perfect infinitive: (to) have + past participle​

Perfect infinitives can have the same kind of meaning as perfect tenses (see here) or past tenses ( (see here).

  • It’s nice to have finished work for the day. (= 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 here).

Passive infinitive: (to) be + past participle​

Passive infinitives have the same kind of meaning as other passive forms (see here).

  • 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 here).

  • There’s a lot of work to do / to be done.

Combinations: to have been sitting; could have been killed​

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?’ ‘I’d like to be being massaged.’

Progressive perfect passive infinitives (e.g. It must have been being built at the time) are very unusual.

Negative forms: Try not to be late.​

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 don’t be late.
  • You were silly not to have locked your car.
  • He’s very busy. I’m afraid he can’t be disturbed.

to​

Note that the infinitive marker to (as in He wanted to go) is not a preposition. After the preposition to we use -ing forms (see here).

For the use of to instead of a whole infinitive (e.g. I’d like to), (see here).

Split infinitive: to really understand​

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. There is an old rule which says that split infinitives are incorrect. This is not true, but people who believe in the rule try to avoid split infinitives by putting the adverb in another position.

  • He began slowly to get up off the floor.