The infinitive is the root form of the verb. There are two kinds of infinitive: the to-infinitiveg. to buy, to get and the bare infinitive which is the root of the verb without to e.g. buy, get.
We use the to-infinitive after verbs such as:
We decided to go to Hawaii.
I hope to find a well-paid job soon.
We plan to go to Europe this summer.
I want to study French.
Be + adjective
We use the to-infinitive after be + adjective.
easy / difficult / impossible / dangerous / safe / expensive / interesting / nice / wonderful / terrible etc.
It’s nice to see you again.
It’s very difficult to work long hours.
It wasn’t easy to find the way.
We also use the to-infinitive after some verbs such as know, learn, remember, ask, want to know, etc. when there is a question word (who, what, where, how, etc.)
I don’t know what to do.
They asked how to get to the bank.
Remember that why is not followed by an infinitive, but by a subject + verb.
I didn’t know why she was talking to me like this.
Too and enough
We use the to-infinitive after too and enough
It’s too late to change anything.
They aren’t old enough to travel alone.
Something / anybody
We use the to-infinitive after something / anybody
I’m thirsty. I want something to drink.
I need somebody to talk to about my problems.
We use the bare infinitive after the modals.
You can stay at home if you don’t feel like going out.
You may go now.
Let and make
We also use the bare infinitive after the verbs let and make.
My parents make me clean my room once a week.
My parents sometimes let me stay overnight at my friend’s.
Subject of the Infinitive
When the subject of the main verb and the subject of the infinitive are the same, then the subject of the infinitive is omitted.
I want to be rich and famous.
I would like to visit China one day.
Sometimes the action of the infinitive may be done by a different person or thing than the subject of the sentence. This doer of the infinitive’s action follows the verb and comes before the infinitive. This is known as the subject of the infinitive. It can be a name (Chris), a noun (the children) or an object pronoun (me, you, them, etc.). Keep in mind that when an infinitive follows a verb, sometimes the word to is dropped from the infinitive.
We wanted Bill to go to the airport.
Simon helped me (to) do my home work.
Too versus Enough
Enough has a positive meaning. It means “sufficient”, or “as much or many (of something) as necessary”.
Enough comes after adjectives and adverbs and is followed by to – infinitive.
adjective / adverb + enough + to – infinitive
The water is warm enough to go for a swim.
We aren’t driving quickly enough to catch the train.
Enough comes before nouns.
enough + noun to – infinitive
We’ve got enough money to buy a house.
Too has a negative meaning. It means “more than enough” or “more than is needed or wanted”.
Too comes before adjectives and adverbs and is followed by to – infinitive.
too + adjective / adverb +to – infinitive
The water is too cold to go for a swim.
We are driving too slowly to catch the train.
We also say too … for somebody / something + to – infinitive. Remember that we do not repeat the pronoun defining the subject.
The suitcase is too heavy for him to lift. (not to lift IT)
The jacket is too big for me to wear. (not to wear IT)
When we put too before nouns, it goes in the expressions too much and too many. Too much is used before uncountable nouns. Too many is used before countable nouns.
You put too much sugar in my coffee.
There are too many people to fit in the car.