Infinitive clause

1. Kinds of infinitive clause

There're two kinds of infinitive clause:
(1) The to-infinitive clause, in which the verb follows to (to + Verb)
(2) The bare infinitive clause, in which the verb does not follow to (Verb) is much less common.

The infinitive clause is called a "clause" because it can have clause elements such as subject, object, complement, and adverbial, as well as an infinitive verb phrase. Let's see the table below:

	subject	verb phrase	object	complement	adverbial
It's best		to | write	those letters		immediately.
It's best	for us all	to | be		ready	by 5 o'clock.
It's best		to | clean	the house		thoroughly.
It's best	for the job	to | be done			by an electrician.
It's best		to | be finishing	the work		when he arrives.

As we see in the table above, infinitive clauses usually have no subject. When they do have a subject, it usually comes after the word for.

An infinitive clause is similar to a finite subordinate clause - for example, a That-clause or an If-clause - as these examples show.

(1) I'm sorry to have spelt your name wrongly.
means the same as:
I'm sorry that I spelt your name wrongly.

(2) It's best for us all to be ready by 5 o'clock.
means the same as:
It's best if we are all ready by 5 o'clock.

2. How to use to-infinitive clauses

To-infinitive clauses have many uses. Here are the main ones:

2.1. To-infinitive clauses follow some verbs (as object)

To-infinitive clauses follows these verbs: begin, expect, hope, learn, like, want, etc.
Form: ... Verb + To + Verb (...)
Ex: I hope to see you soon. Sam's learning to drive.

They also follow some linking verbs as complement, for example, be, seem, appear.
Ex: This timetable seems to be out of date.

See Verb pattern 7 for more details.

2.2. To-infinitive clauses follow the object after some verbs

After some of these verbs such as ask, consider, expect, tell, etc., the to-infinitive follows the object.
Form: ... Verb + Object + To + Verb (...)
Ex: Sam expected his friends to arrive late.

See Verb pattern 17 for more details.

2.3. To-infinitive clauses follow some adjectives

The to-infinitive clauses follow some adjectives such as easy, hard, difficult, ready etc.
Form: ... Adjective + To + Verb (...)
Ex: This truck is difficult to drive.

See Adjective pattern for more details.

2.4. To-infinitive clauses follow some abstract nouns

Form: Noun + To + Verb (...)

(a) Nouns which come from verbs or adjectives:
Ex: Sam mentioned his desire/wish to work overseas.

(b) General nouns like time, way, place, reason:
Ex: It'll soon be time to go home.

2.5. To-infinitive clauses follow some common nouns or pronouns

The infinitive is similar in meaning to a relative clause. The meaning is one of purpose.

Form: Noun / Pronoun + To + Verb (...)
Ex: Can I borrow something to read?

Note: Sometimes there is a preposition at the end of the clause which links back to the noun or pronoun.
Ex: Could I have someting to sit on?

2.6. To-infinitive clauses can follow TOO or ENOUGH

To-infinitive clauses can follow too or enough, usually with a word between:
Form: TOO ... / ENOUGH (...) + To + Verb (...)
Ex: Sam gave me too much to eat.

2.7. To-infinitive clauses can act as subject

More usually, the to-infinitive is a "delayed subject" at the end of a clause beginning with it.

Form: To + Verb (...) + Verb (...)

Ex: To prove her guilt would be be very difficult. (To prove her guilt here is a subject)

Also:

It + Verb (...) + To + Verb (...)
(1) It would be very difficult to prove her guilt. (to prove her guilt here is a "delayed subject")

(2) It's a pity to be so mean. (to be so mean here is a "delayed subject")

For more details, see End weight, Given and New.

2.8. To-infinitive clauses can act as an adverbial

To-infinitive clauses can act as an adverbial, especially of purpose (answering the question why? or what ... for?).
Ex: "Why did you get up so early?" "To meet my family at the airport."

In formal style, we add in order or so as before to:

Form: Clause + (in order / so as) + To + Verb (...)

(1) They are introducing new labour laws, (in order) to improve the performance of industry.

(2) The sea wall must be repaired, (so as) to prevent further flooding.

3. Using bare infinitive clauses

Bare infinitive clauses are much less common than to-infinitive clauses. Some examples of the use of bare infinitive clauses are:

3.1. After the verb help, had better, or would rather

Bare infinitive clauses are used after the verb help, or after a verb idiom such as had better, or would rather. [see Verb pattern 8]
(1) This medicine helps keep us healthy.*
(2) We'd better be careful.

3.2. After the object after some verbs

Bare infinitive clauses are used after the object after some verbs, for example, make, see, hear, let. [see Verb pattern 18]
Ex: The book was so sad, it made her cry.

3.3. After all / what + subject + verb (...) do + be ...

(1) All he did was report the accident.*
(2) What he's done is mend the water pipe.*

3.4. After rather (...) than (expressing preference)

(1) I'd rather work at the home than travel forty miles to work every day.
(2) Sam prefers to do his own repairs, rather than take the car to a garage.*

* These sentences could also have a to-infinitive, instead of a bare infinitive; for example, to keep, to mend, to report, to take.

I hope this article helps. If you have any question, please leave a comment below.