This sentence looks simple enough, right?
All you have to do is take a rest.
I’m having trouble analyzing it though. Is the subject all or you? Is the main verb the modal “have to” or “is”?
It seems to be a double sentence. How can I explain the reason why “is” is next to “take” in this sentence?
thx
All you have to do is take a rest.
Take a rest = X.
[All you have to do is X] = X is [what] you have to do.
“[what] you have to do” is a noun phrase.
In the original form, the grammatical subject is “All you have to do” which is a shortened form of “All of the things that you have to do” or something similar (in deep structure).
“Is” is next to “take” because the infinitive “to” has been deleted. You could also say ( and the deep structure form of the sentence would be) “All that you have to do is to take a rest.” Infinitives often act as nouns or noun-like things: “To eat 15 hotdogs in one minute is difficult.” “To err is human”…etc. etc.
Gosh, that’s about all I got out of my required morphology/syntax classes, sad to say.
well thx 
Good answer from Ironlady. You can also approach it from this angle:
To make ‘all’ seem more noun-like, think of ‘all’ as equivalent to ‘the only thing’. It’s the subject.
‘You have to do’ is an abbreviation of ‘that (or ‘which’) you have to do’; this relative clause merely modifies the subject. Its verb isn’t relevant to the main SV pattern of the sentence.