Michael Swan (Practical English Usage,OUP) writes;
pre-conditions: If we are to get there in time ...
The structure is common in if-clauses, when the main clause expresses something that must happen first if something else is to happen
If we are to get there by lunchtime, we had better hurry.
He knew he would have to work hard if he was to pass his exam.
I am really sorry.
I know to believe is an infinitive and you have also told me in post number 6.
Why did i ask this question because infinitive can function as an adverb, noun etc.
If some one says : I am to go. it can mean sometthing is missing between be + infinitive and is understood. Example I am pasting below.
I am/you are/he is/they are, etc. + infinitive means intention, expectation, supposition or requirement.
For example :
I am to go to the principle's office right now = I am supposed to go/expected to go/required to go.
I am to direct the visitors = I am expected/required to direct the visitors.
I was/you were/they were, etc. + perfect infinitive means intention, supposition, etc. in the past.
likewise if we say :
If we are to believe,
is there something missing between be and infinitive in this case.
How is this infinitive functioning here.