There are different types of infinitive in English.
The most common is the "to do" form of the verb, as in "I want to study English", which we use after many verbs.
There's also the "bare infinitive" (infinitive without "to") which we use after modal verbs, other auxiliary verbs, or certain other verbs in the active voice, such as make or let.
Other types of infinitive are the continuous infinitive ("He wants to be working as a teacher by next year"); the perfect infinitive ("I'm sorry, but I seem to have forgotten your name") and the passive infinitive ("He hopes to be selected for the short list").
Verbs that take the infinitive
Here are some common verbs which you must follow with the infinitive ("to do"):
afford, agree, appear, ask, attempt, beg, choose, decide, deserve, expect, forget, help, hope, intend, offer, plan, promise, refuse. threaten, want, wish.
Some of the verbs above can also be followed with an object and an infinitive:
ask someone to do
beg someone to do
choose someone to do
expect someone to do
want someone to do
These verbs are followed by an object and an infinitive:
advise, allow, encourage, force, forbid, invite, order, permit, persuade, teach, tell, warn.
Some verbs, such as continue, begin and start can be followed with the infinitive or gerund with no change in meaning.
For verbs that take the gerund, as well as verbs that take both, see our page on gerunds.
Adjectives and infinitives
You can use an infinitive after an adjective. For example:
"I'm happy to help you."
"English is easy to understand."
"It's lovely to sit in the garden."
To do / for + ing
When you talk about how you use something (often on a particular occasion), use the "to do" form.
"Use these scissors to cut this paper."
"Here - use this bowl to put the sugar in."
When you talk about the general purpose of an object, use for + ing.
"These scissors are for cutting material."
"We use the other remote for changing channels."
Also use the infinitive to talk about purpose.
"He studied hard to pass the exam." (Sometimes you'll see "in order to", as in "He studied hard in order to pass the exam."
If you want to make the infinitive negative, put the "not" before "to".
For example, "I decided not to apply for the job" and not "I decided to not apply for the job".
Many English grammar experts say that putting an adverb between the "to" and the rest of the infinitive is bad writing style. Where possible, you can put the adverb at the end of the sentence so you don't separate the two parts of the infinitive.
For example: "He decided to quickly eat lunch" becomes "He decided to eat lunch quickly."