Verbals

Infinitives

An infinitive (to visit, to forgive) has no tense, but it can do a noun’s job, modify another word, or complete a verb, as in have to leave. It is the first of three non-finite forms, and its to makes it the easiest to recognise.

What you’ll learn

Tell an infinitive from a prepositional phrase that starts with to
Name the slot an infinitive phrase fills, such as subject, direct object, objective complement or appositive
Draw an infinitive phrase on a pedestal when it fills a noun slot
Tell adjectival, adverbial and complementary infinitive phrases apart
Draw an infinitive's own object on the infinitive's line, not on the base line
Correct four common mistakes with infinitives

The infinitive: to + the base form of a verb

An infinitive is to plus the base form of a verb: to visit, to forgive, to run. It carries no tense, so it is never the verb phrase of a clause.

But to is also a very common preposition. To tell the two apart, look at the word after to:

She hopes to visit Lisbon. — the base form of a verb: an infinitive.
She travelled to Lisbon. — a noun: a prepositional phrase.
She objects to paying twice. — an -ing form: a prepositional phrase too, with a gerund as its object. So objects to pay is wrong.

Infinitive after a verb: the direct object

The most common position is after a verb such as want, hope, try, need, decide or plan. Ask the question that finds a direct object: She hopes what? The answer is the whole phrase, to visit Lisbon.

So the infinitive phrase is the direct object. The diagram puts it on a pedestal, a small stand that holds a whole phrase in one slot. The foot of the pedestal is in the object slot, after the same half vertical a noun object gets.

A few verbs are different. After wait, agree, hurry, stop and some others, the infinitive is not an object. It hangs below the verb as an adverbial infinitive: We can’t wait to leave, The customer agrees to pay.

In the Roles exercise, to visit Lisbon gets two labels: Direct object for its job and Infinitive phrase for its form.

“She hopes to visit Lisbon.”

Reed-Kellogg — the infinitive phrase on a pedestal in the direct-object slot

nsubj Nominal subject
ROOT Root of the sentence
aux Auxiliary
xcomp Open clausal complement
dobj Direct object

Dependency — xcomp, with its own object

Comparing the two views

The diagram shows the phrase as one unit: all of to visit Lisbon stands on one pedestal in the direct-object slot. Lisbon sits on the infinitive’s own line. The tree has no unit for the whole phrase. It makes visit an xcomp (“open clausal complement”) of hopes, and Lisbon the dobj of visit. The label adds one thing the diagram does not say: an xcomp borrows its subject, so She is also the one who visits.

Infinitive as the subject

An infinitive can also be the subject. In To forgive takes courage, ask what takes courage. The answer is to forgive, so the whole infinitive is the subject.

The pedestal works here too: it stands in the subject slot and says “treat this whole phrase as one noun”.

An infinitive subject sounds formal. Everyday English more often uses a gerund, as in Forgiving others takes courage, or starts with It: It is hard to forgive others. The next section explains this use of It.

Find the verb phrase
It is takes. The rest of the sentence fits around it.
Ask what takes courage
The answer is to forgive, both words. That is the subject.
Put the infinitive on a pedestal in the subject slot
The pedestal puts the whole phrase in one slot. To goes on the diagonal and forgive on the line above the stand.

“To forgive takes courage.”

Reed-Kellogg — the infinitive raised on a pedestal

aux Auxiliary
csubj Clausal subject
ROOT Root of the sentence
dobj Direct object

Dependency — csubj, no elevation needed

Comparing the two views

Reed-Kellogg needs a special mark, the pedestal, to put a whole phrase in the subject slot. The tree needs nothing special. It makes forgive the csubj (“clausal subject”) of takes and attaches it like any other subject, with To below it as aux.

Two more slots: objective complement and appositive

Two common patterns put an infinitive phrase in a slot you met on earlier pages. The Roles exercise gives the phrase its form label, Infinitive phrase, and a slot label.

Verb + object + infinitive. After ask, tell, want, expect or allow, the object comes first and the infinitive follows it: The coach told us to stretch. The phrase is an objective complement. The diagram stands it on a pedestal after the backslash, and the Roles exercise boxes us as the Direct object and to stretch as an Obj. complement. With tell and ask, the person can look like an indirect object, as in told us a story. Before an infinitive, Grammify calls it the direct object; some grammars disagree.
It + be + adjective + infinitive. It fills the subject slot, and the infinitive phrase at the end says what It means: It is easy to make mistakes. The phrase is an appositive to It. Its pedestal stands in parentheses after It, and the Roles exercise boxes it as an Appositive.

“The coach told us to stretch.”

Reed-Kellogg — the infinitive phrase on a pedestal after the backslash

det Determiner
nsubj Nominal subject
ROOT Root of the sentence
dobj Direct object
aux Auxiliary
xcomp Open clausal complement

Dependency — dobj for the object, xcomp for the infinitive

Comparing the two views

Reed-Kellogg gives the phrase a slot of its own: to stretch stands on a pedestal after the backslash. The backslash points back to us, the direct object. The tree has no slot for it. It makes stretch an xcomp of told, as it did with visit in She hopes to visit Lisbon. An xcomp borrows its subject, but the label does not say from which word. Here it comes from us: we stretch, not the coach.

After make, let, see and hear (and often help), the infinitive after the object has no to: Our guide let us touch the statue. This is a bare infinitive. It is still an infinitive phrase and an Obj. complement, not a verb phrase. In the diagram, the diagonal where to would stand is empty. A base form after a modal is different: must leave is one verb phrase.

Adjectival and adverbial infinitive phrases

An infinitive phrase can also modify, the way an adjective or an adverb does. It then hangs beneath the word it modifies on the shape a prepositional phrase uses: to on the diagonal, the verb on the horizontal.

Modifying a noun or pronoun, it is an adjectival infinitive phrase. It tells you which one or what kind: a place to sleep, nothing to do, the right to vote.
Modifying a verb, adjective or adverb, it is an adverbial infinitive phrase. Most often it says why: ran to catch the bus, happy to help, too tired to walk.

One sentence can show all three kinds of attachment: We have nothing to do, we are ready to go, and we can’t wait to leave.

To do modifies the noun nothing: an adjectival infinitive.
To go modifies the adjective ready: an adverbial infinitive.
To leave modifies the verb can’t wait: an adverbial infinitive.

The Roles exercise gives each one a single label, Adjectival infinitive phrase or Adverbial infinitive phrase, because the name already says the job.

“Mia found a place to sleep.”

Reed-Kellogg — an adjectival infinitive hangs from its noun

nsubj Nominal subject
ROOT Root of the sentence
det Determiner
dobj Direct object
aux Auxiliary
relcl Relative clause modifier

Dependency — the infinitive is a relcl of place

Comparing the two views

Both views attach to sleep to place, the noun it describes. Reed-Kellogg hangs it there the way it hangs a prepositional phrase. The tree labels it relcl, the relation for a relative clause, because a place to sleep means a place where she could sleep. The parser reads the infinitive as a short form of that clause.

“Leo ran to catch the bus.”

Reed-Kellogg — an adverbial infinitive hangs from its verb

nsubj Nominal subject
ROOT Root of the sentence
aux Auxiliary
advcl Adverbial clause modifier
det Determiner
dobj Direct object

Dependency — advcl, the label for an adverbial clause

Comparing the two views

Both views attach the infinitive to ran. Here the tree’s label says more: advcl, an adverbial clause, tells you that the phrase works like an adverb. In this sentence, it says why he ran. Both views also show that bus belongs to catch. The tree makes it the dobj of catch, and the diagram puts it on the infinitive’s own line, after its own half vertical.

Complementary infinitive phrases: have to, ought to, used to

A few verbs work almost like modals: have to, have got to, ought to, used to, be going to, be supposed to and be to. The infinitive after them completes the verb, the way a main verb completes must or will. This is a complementary infinitive: an infinitive used to complete certain modal-like verbs.

In I have to see the shipment that came in today, the complementary infinitive phrase is to see the shipment that came in today. Inside it, the shipment that came in today is the object of see, not of have.

EFL coursebooks call these pairs phrasal modals. To test one, put a modal and the base form in its place. If the meaning stays about the same, the infinitive is complementary:

I have to see ≈ I must see
You are supposed to stay ≈ You should stay
We are going to go ≈ We will go

The drawing is the verb, then a pedestal with no divider in front of it, because the infinitive is not the verb’s object. The verb keeps its own Verb phrase box: has, ought, are going. The Roles exercise labels the infinitive and everything after it Complementary infinitive phrase, with no slot label beside it.

For tense, the first verb decides: used to and had to are past, has to is present, and ought to has no tense, like a modal. Be going to is the exception. The Tense filter reads are going to go as one future, although the drawing and the Roles exercise split it after going. With was or were, as in was going to call, the verb phrase has no tense.

“Sam has to feed the cat.”

Reed-Kellogg — a complementary infinitive, with no divider after the verb

nsubj Nominal subject
ROOT Root of the sentence
aux Auxiliary
xcomp Open clausal complement
det Determiner
dobj Direct object

Dependency — the same xcomp as after hopes

Comparing the two views

Nothing separates has from its pedestal: the phrase completes the verb but is not its object. The tree cannot show this. It makes feed the xcomp of has, just as visit is the xcomp of hopes, so only the Reed-Kellogg diagram tells the two apart. The tree does show that cat belongs to feed: has has no object at all.

Be to needs care. It is complementary when it means must or is scheduled to: The wedding is to be held in an azalea garden. But after a subject such as goal or plan, the infinitive says what the subject is. Then it is a predicate nominative: My goal is to win, like To love is to live fully.

The Roles exercise decides by the subject. When the subject is a goal-type noun (goal, aim, plan, job, way, step, thing…), a verbal or a clause, it expects Pred. nominative. After any other subject, it expects Complementary infinitive phrase: The moment is to act. After a noun, a passive infinitive is always complementary, even after plan: The plan is to be announced tomorrow.

Common mistakes with infinitives

Four mistakes are common with infinitives. The first three come from Spanish.

After want, use an object and an infinitive. Diego wants us to wait, not Diego wants that we wait (Spanish: Diego quiere que esperemos). For more Spanish subjunctives and their English forms, see English uses fewer subjunctives on the Mood page.
Start with It. It is necessary to bring a dictionary, not Is necessary to bring a dictionary (Spanish: Es necesario traer un diccionario). An English clause needs a subject, and It fills the slot.
Use to, not for, to say why. I went to the market to buy bread, not for buy bread or for to buy bread (Spanish: para comprar pan).
No to after a modal. You must wear a helmet, not You must to wear a helmet. The same is true after let or make and an object: let us touch, not let us to touch. But have to keeps its to: You have to wear a helmet.

Quick check

Nina walked to the station to buy a ticket. Which to starts an infinitive, and which starts a prepositional phrase? How can you tell?
Answer
The second to starts an infinitive, because the base form of a verb, buy, comes after it. The first starts a prepositional phrase, because a noun phrase, the station, comes after it. The Tags exercise agrees: the first to is IN and the second is TO. To buy a ticket says why she walked there, so it is an adverbial infinitive phrase.
Name the kind of infinitive phrase in each sentence: Diego has no time to cook. Omar stayed late to finish his work. Omar ought to finish his work.
Answer
To cook is adjectival: it modifies the noun time and answers what kind of time? In the second sentence, to finish his work is adverbial: it says why Omar stayed late, and in order fits in front of to. In the third, it is complementary: ought to finish means about the same as should finish, so its pedestal stands straight after ought, with no divider.
Marta wants to learn French. Marta has to learn French. Both trees make learn an xcomp. How do the two Reed-Kellogg diagrams differ, and where does French go in each?
Answer
After wants, the infinitive phrase is the direct object (Marta wants what?), so its pedestal stands after a half vertical. After has, it is a complementary infinitive (has to ≈ must), so the pedestal stands straight after the verb, with no divider. In both, French is the object of learn: it goes on the infinitive’s own line, after its own half vertical, not on the base line.
Correct these two sentences, and say what job each infinitive phrase does: My brother wants that I help him. Is easy to get lost in this city.
Answer
My brother wants me to help him. After want, English uses an object and an infinitive, not a that clause. Me is the direct object, and to help him is an objective complement. It is easy to get lost in this city. An English clause needs a subject, so It fills the slot. The infinitive phrase at the end is an appositive: it says what It means.

Key terms

Infinitive: To plus the base form of a verb. It carries no tense, so it cannot head a clause on its own. The to is tagged TO, relation aux. Without to, it is a bare infinitive. She wants to leave. To forgive takes courage.
Infinitive phrase: The infinitive with its own objects and modifiers, working as one unit. A lone infinitive is a one-word infinitive phrase. When the phrase fills a slot, the Roles exercise adds that slot’s label: Subject, Direct object, Pred. nominative, Pred. adjective, Obj. complement or Appositive. She wants to leave early. To own her own car has long been her desire.
Bare infinitive: An infinitive without to, after the object of make, let, see, hear or help. It is still an infinitive phrase, not a verb phrase. Our guide let us touch the statue. We heard the baby cry.
Adjectival infinitive phrase: An adjectival infinitive phrase modifies a noun or pronoun. In the diagram, it hangs beneath that word, the way a prepositional phrase would. Mia found a place to sleep. We have nothing to do.
See: Modifier Relations
Adverbial infinitive phrase: An adverbial infinitive phrase modifies a verb, an adjective or an adverb. Most often it says why. In the diagram, it hangs beneath the word it modifies. Leo ran to catch the bus. I am happy to help.
See: Modifier Relations
Complementary infinitive phrase: The infinitive phrase that completes have to, have got to, ought to, used to, be going to, be supposed to or be to, the pairs EFL books call phrasal modals. It is drawn on a pedestal straight after the verb, with no divider. Sam has to feed the cat. You ought to rest.
Pedestal: A pedestal is a stand that raises a whole phrase or clause into one slot of the diagram. Infinitive phrases, gerund phrases and noun clauses all use it. To forgive takes courage. — the infinitive subject stands on a pedestal. She likes to swim. — so does an infinitive object.
See: Reed-Kellogg Diagrams · Gerunds · Noun Clauses
xcomp: “Open clausal complement” — the relation for an infinitive completing another verb, with its subject supplied by the main clause. She wants to leave. — leave is the xcomp of wants. They began to sing.
See: Core Arguments

Practice on a real sentence

This sentence has no infinitive, so use it for contrast. Every verb phrase in it has a tense: in the Tags exercise there is no TO, and each verb phrase starts with a past form, VBD. In the Dependencies exercise, each verb phrase has its own subject, an nsubj. The infinitive in She hopes to visit Lisbon has neither: visit has no tense and no nsubj.

Loading the practice sentence…