Grammar Help

[5jj]

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.

[rajan]

If we are to believe - Does "to believe" function as an adjective.

We are supposed to believe him - does to believe function here as an adverb.

1) "If we believe" suggests that it's probably something we already believe. "If you believe that, you'll believe anything".

2) "If we are to believe" suggests that there is a possibility that we won't believe whatever it is.

If I believe that I can lose weight, then I can! = Provided that I believe...

If I am to believe what my friend says, she lost 12kg in a week = If I choose to believe what she says, then... (I have to decide whether or not to believe her.)

[5jj]

If we are to believe - Does "to believe" function as an adjective.

We are supposed to believe him - does to "believe: function here as an adverb.

Now you are simply not thinking.

"To believe" is the ti-infinitive form of the verb. See post #6.

[rajan]

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.

Now you are simply not thinking.

"To believe" is the ti-infinitive form of the verb. See post #6.

[5jj]

If someone says : "I am to go". it can mean sometthing is missing between be + infinitive and is understood. Example I am pasting below.
Nothing is missing. [...]
)
For example :

I am to go to the principleal's office right now = I am supposed to go/expected to go/required to go.
You are giving expressions with similar meangs, not showing what is 'missing'. [...]

likewise if we say :

If we are to believe,

is there something missing between "be" and infinitive in this case. No
.

am/are/is/was/were to'(there is no infinitive form be to) is a quasi-modal verb in it own right.