The infinitive form of a verb is the basic dictionary form of a verb used without inflection or tense and usually (but not always) preceded by ‘to’, for example “to drink,” “to eat,” “to write.”  Unlike verb tenses (verbs that are conjugated) infinitives do no tell about the time of actions or events or who is completing the action.  Infinitives are most often used together with other verbs (that are conjugated) to refer to actions and events in a more general way.

Here are some examples:

Beth hopes to move to the United States.
James doesn’t want to be here.
We are happy to welcome you to our country.
He just started to study when the doorbell rang.
Children love to play outside.

As I mentioned, infinitives in general are almost always preceded by the word ‘to,’ as this marks the verb as an infinitive, but there are, of course, exceptions to this rule, which I have outlined below.

1) Do not include ‘to’ before an infinitive after modal auxiliary verbs.  Modal auxiliary verbs are: shall, will, would, should, can, could, may, might, and must.

Examples:
I must go now. not I must to go now.
She will be elected. not She will to be elected.

2) The following verbs: let, make, see, hear, feel, watch and notice, when followed by an object are not followed by ‘to’ + infinitive, they just take the infinitive, without the ‘to’.

Examples:
The teacher——-let—————-them————study————-before the exam.
Subject—–(exception verb)—–object———(infinitive)——–prepositional phrase.

I didn’t see you come in.  not I didn’t see you to come in.

3) When asking a questions with why or why not ‘to’ is not used before the infinitive verb.

Examples:
Why pay more, when you can pay less? not Why to pay more, when you can to pay less?
Why not take the holidays off from work? not Why not to take the holidays off from work?

4) When two infinitives are joined by: and, or, except, but, than, as, or like, the second infinitive usually goes without the ‘to’.

Examples:
It is as easy to smile as frown. not It is as easy to smile as to frown.
I want to have lunch now and wash the dishes later. not I want to have lunch now and to wash the dishes later.

5) Expressions with do and did, like “all I did…” or “what I do…” do not need the ‘to’ before the infinitive verb.

Examples:
What I do is greet the customers when the come in the store.  not What I do is to greet the customers when the come in the store.
All he did was answer the door. not All he did was to answer the door.

I hope that all makes sense.  Remember for the most part an infinite verb is proceed by ‘to’ which make it as an infinitive.  Now here is some practice with infinitives, be sure to pay special attention to the rules presented above.  You have to decide if ‘to’ should go in front of the infinitive verb or not.  Good luck!  The answers are below, so don’t scroll all the way down to the answers until you are done.

1. I will (to) go alone.
2. Penelope wants (to) study with her friends
3.Why stand up if you can (to) sit down?
4. We offered (to) watch my sister’s children for the night.
5. What I do for work is (to) organize all the mail that comes in.
6. They want (to) visit the White House while they are in Washington, DC.
7. It is easier (to) do it myself.
8. We asked him (to) sing his national anthem.
9. I didn’t see you (to) come in.
10. She wants (to) dance with you.

Answers:
1. I will go alone. – no ‘to’
2. Penelope wants to study with her friends
3.Why stand up if you can sit down? – no ‘to’
4. We offered to watch my sister’s children for the night.
5. What I do for work is organize all the mail that comes in. – no ‘to’
6. They want to visit the White House while they are in Washington, DC.
7. It is easier to do it myself.
8. We asked him to sing his national anthem.
9. I didn’t see you come in. – no ‘to’
10.  She wants to dance with you.