photo credit: ical tefl (license)

The Infinitive is the base form of the verb‏‎:

be, have, walk…

Often the infinitive is introduced by the particle, to:

to be, to have, to walk…

Note that when the infinitive is on its own it’s sometimes known as the Bare Infinitive; when it’s with to then it’s sometimes known as the Full Infinitive.

Full Infinitive Usage/Infinitive Clauses

We use the full infinitive (the infinitive with to) as a noun, adjective‏‎ or adverb‏‎ phrase. They are sometimes known as Infinitive Clauses.

To be or not to be.

To put it bluntly: you’re wrong!

To pay for the mortgage, he took a second job.

I want to go to Japan.

A common question and answer expressing purpose is like this:

Statement: I’m packing my bag.

Question: Why now?

Answer: To save time later.

Bare Infinitive Usage

We use the bare infinitive in a number of different ways.

1) After most modal‏‎ and auxiliary verbs:

{modal/auxiliary} + {infinitive}

We should + go now.

They must + arrive soon.

Note that the main exception here is the modal ought to.

2) With some verbs of perception‏‎:

{verb of perception} + {object} + {infinitive}

I watched it explode.

I heard them shout.

Double Infinitive

Sometimes we need to use more than one infinitive in a row:

A picture can be useful to help to explain what happened.

Although correct grammatically, this can sometimes sound a little awkward and we can say instead:

A picture can be useful to help and explain what happened.

Alternatively, we can say:

A picture can be useful to help explain what happened.

These are all correct.