The subjectThe person or thing that performs the action of a verb or that is described by a verb. E.g.: Andy has never been to Brunei. ("Andy") of the actionA general term expressing that somebody or something does something. expressed by an infinitive is usually the nearest preceding nounA part of speech that names a person, place or thing. E.g.: The koala is a marsupial. ("koala", "marsupial") phrase or pronounA part of speech that refers to or stands instead of a noun. E.g.: Who do you think I am? ("you", "I").

I want to go home.
My grandfather is known to like red wine.
You had to go home.
This sonnet must have been written by Shakespeare.
I’d rather be writing my thesis now.
I want you to go home.
I have come here to help you.
I have come here in order for you to be happy.
It was quite difficult for me to understand what he was saying.
I saw him cross the street.

However, there are cases when this is not so:

To tell the truth, I don’t really like your cooking. (the subject does not precede the infinitive)
It’s easy to speak like that! (the subject of to speak is not it!)
To accept the truth is sometimes difficult. (the subject of to accept (people) is not mentioned)
I have something to tell you. (the subject of to tell is not the nearest preceding noun something)

Diagrams

The subject of non-finite forms
The subject of non-finite forms The subject of participles