Can "will" be used with "if"?

Question

In a book I read a line if you will forgive us, our lunch is growing cold

I know that in 1st condition of English, we use present simple. Then why "will" is being used here.

Answer 1

Note that "If you will come over here I will tie your shoe for you" is perfectly legitimate English. It's not (necessarily) and "idiom".

Answer 2

"If you will" is an idiomatic phrase in this case:

Said when politely inviting a listener or reader to do something or when using an unusual or fanciful term. [Lexico]

The applicable part of this definition is "inviting a listener or reader to do something."

We aren't talking about the first conditional. Instead, we are using an idiomatic phrase.

Essentially, this sentence means:

Please excuse us. We need to leave because our lunch is becoming cold.

If you want to read about the non-idiomatic uses of "will" in "if" clauses, please read THIS or THIS.

Answer 3

When will is used in an if-clause, it is restricted to its Deontic sense, which means 'be willing to'.

So common politeness formulas with if, like

• If you will forgive us, ...,
• If you would allow us to ...,
• If you will give me a moment ...,

mean

• If you are willing to forgive us, ...

etc. That makes more sense in expressing politeness; asking for permission saves face.

Every modal verb (and will and would are modal verbs, not future tenses or conditional moods) has at least two kinds of meaning.

One kind of modal verb meaning (called the Epistemic sense of the modal) is intransitive and has to do with the speaker's judgements about likelihood and probability. The epistemic sense of will is the speaker's judgement about the most likely future.

• She will arrive around four.
• I'll get some bread on my way home.
• Nobody will notice it.

That's why the modal auxiliary verb will is often mistakenly called the English "future tense", even though it's not the most common way to refer to the future.

The epistemic sense of will is not allowed in if clauses, however. This is just an arbitrary rule of English, but it highlights the other sense of will.

The other kind of meaning that modals have is called the Deontic sense, and it's transitive, in the sense that it has to do not with logical possibilities but with social obligations and permissions. There is a relation between the agent subject and some other social force, which may be a person, a law, or a habit.

The root of the verb will is the same as the noun will, and the adjective willing. A will is a written record of what you want done with your property when you die. God's will refers to what God wants. Will means want, and that's the only meaning allowed in if clauses.

It's also common in negatives.

• He won't unlock the door

is not a prediction of the future, but a statement about his refusal.

And it's also present as an unspoken presumption about any prediction involving humans --
someone will do something only if they're willing to do it.

Answer 4

This is idiomatic in (formally polite) spoken language. You can think of it as short for "If you will forgive us, we will take our leave, since our lunch is growing cold".

The "we will take our leave" part is implied. The "if" is a way of saying -- in theory -- that we will only take our leave if you agree to forgive us for doing so. The future tense ("will") is used because they haven't yet agreed to give their forgiveness. Again, this is very formally polite language.