Phrase: The visitors forgot to give their address.

[Ashish1354]

The visitors forgot to give their address.

I need to understand
what does the above infintive phrase modify?
How could i spot what a phrase describes?
Does an Infinitive Phrase always behaves like a noun?

[Mister Micawber]

.
Just think about it-- 'to give their address' tells what they forgot, so it is the object of 'forgot'. Infinitives don't always act like nouns, though they often do. I went to London to see the Queen-- here, its an adverb. My favorite way to travel is by ship-- here, it is an adjective.
.
_________________
Native English teacher at Mister Micawber's