Confusing use of "if" in "Advanced Grammar in Use"

Question

I'm currently leafing through Advanced Grammar in Use by Martin Hewings and on page 18 there is a unit (unit 9) describing the difference between "will" and "be going to". Among other rules, there is this pair of sentences:

I'm going to open a bottle of lemonade, if you want some. (= I'm going to open a bottle of lemonade. Do you want some?)

and

I'll open a bottle of lemonade if you want some. (= If you say you want some, I'll open it)

The difference between mentioned "will" and "be going to" is completely clear to me here, but suddenly there is a new puzzle: this "if" in the first sentence. What does this "if" mean here, if it doesn't make any condition on the opening the bottle part - considering that there is no condition in "Do you want some?"? Is this "if" is some short form of "(I wonder) if you want some"? But in this case shouldn't it be a separate interrogative sentence - "I'm going to open a bottle of lemonade. (I wonder) if you want some?". Or maybe there is a completely different explanation... I'm completely puzzled about this "if-not-being-if". And, btw, the use of commas in these two sentences in the book is not clear to me too: there is one in the first sentence but there is no in the second one.

Answer 1

Good observation! There are actually a few uses of "if":

• The canonical case is that whether something happens or is true depends on a condition: "If it rains, you'll get wet." The "if" part (raining) causes or allows the other part (getting wet) to happen.

• Another case is about evidence: "If you see holes in the walls, you have mice." The "if" part is the evidence leading to an inference. (Linguists call this an epistemic conditional.)

• "I have lemonade if you want some": This is a way of saying the information may be useful to the addressee. What is conditioned is the relevance or helpfulness, not factuality, of the information that the speaker has lemonade. (Linguists call this a pragmatic or speech act conditional.)

[citation for the 3 types: Croft (2022), Morphosyntax, p. 529]

Answer 2

See my comment on What type of conditional clause is this?. Yes, often these "if" constructions omit and imply extra words, like "I'm going to open a bottle of lemonade, [and you can have some] if you want some."

There's no comma in "I'll open a bottle of lemonade if you want some," simply because it doesn't need it. The "if" is meant literally, "I will X if you Y." But in a sentence like "I'm going to lunch, if you want to come," the comma helps represent the omitted thoughts, like "I'm going to lunch [and I'm inviting you], if you want to come."

Update: I actually ran across an instance of this while watching Avatar: The Last Airbender a few hours after writing this answer.

I've never seen such a fine specimen of lemur. That beast would fetch me a hefty sum if you'd be interested in bartering.

Obviously the owner's willingness has no direct bearing on the lemur's value; it conflates "if you were to barter it to me, I could resell it for a hefty sum."

Answer 3

Compare:

She's not dating anyone at the moment, if you were wondering whether to ask her to the dance.

She's not dating anyone at the moment, in case you were wondering whether to ask her to the dance.

The subordinate clause provides an explanation for the speaker making the statement in the main clause, which might seem to have been "out of the blue". Without that if-clause, the conversation might go like this:

She's not dating anyone at the moment.

-- Why are you telling me this?

In case you were wondering whether to ask her to the dance.

-- Why do you think I would be wondering that?

Who do you think you're fooling? I see you stealing glances at her every chance you get.

You could reverse the order of the clauses:

If you were wondering whether to ask her to the dance, she's not dating anyone at the moment.

Putting the if-clause up front opens with a context for the ensuing statement in the main clause.

P.S. The implicit unspoken elliptical result of the if-condition is something like "then you may be interested to know", and the main clause declares the fact you might like to know:

If you were wondering whether to ask her to the dance ^{then you may be interested to know} she's not dating anyone at the moment.

Answer 4

Some people take issue with this usage, since strictly speaking, the grammar is nonsense. The kind of logical link you'd expect between the two clauses just doesn't exist. Nevertheless, it's used and understood.

"If you want some" is really modifying some other omitted thing, and there are a few options for what that might be. I think the following is closest to how I personally parse it:

I'm going to open a bottle of lemonade, just so you know if you want some.

I'm telling you that I'm opening lemonade so that, if you want some, you know about it.

But it's possible to keep it much more straightforward:

I'm going to open a bottle of lemonade; if you want some, you can have it.

This is a pretty unique quirk of English, one I'm surprised to see formally prescribed. Even so, your book is correct; this is one of the rare cases where "will" and "[be] going to" contrast in meaning.

Answer 5

In your first example, the clause is non-restrictive and gets a comma. The actual meaning of the sentence is more like "I am going to open a bottle of lemonade, whether you want some or not. Do you want some?" In the second, the clause is restrictive and does not take a comma. The speaker is saying "I will open a bottle of lemonade only if you want some." The restrictive/non-restrictive nature of the clause determines the use of a comma. That's what I was taught many years ago.

Answer 6

The overall offer in either statement is the same:

"Let me know if you want some lemonade and I will serve you some lemonade."

The slight difference is whether the bottle is opened conditionally-on or regardless-of the listener's response.

While the book's rephrasings of the sentences convey the correct implied meanings, it may perhaps be clearer to treat the statements as having made the following omissions/ellipses.

(1a) I'm going to open a bottle of lemonade, if you want some.
(1b) I'm going to open a bottle of lemonade, if you want some (let me know and I'll serve you some).

(2a) I'll open a bottle of lemonade if you want some.
(2b) I'll open a bottle of lemonade (and serve you some) if (you let me know) you want some.

This way it is easier to see that "if" doesn't change in meaning, but rather it is "am going to" and "will" that have different nuance in the sentence.

The nuance of "am going to" in the first pair of sentences is that it is treated as a statement of fact. Regardless of the listener's response the speaker is going to open the bottle either way.

The nuance of the "will" in the second pair of sentences is that it is treated as a promise. Depending upon the listener's response, the speaker either will open the bottle or they won't open the bottle.

---

Another similar example would be:

(1a) I'm going to the store, if you need anything.
(1b) I'm going to the store; if you need anything (you should let me know now what to purchase).

(2a) I will go to the store if you need anything.
(2b) I promise to go to the store if you need me to purchase anything from the store.

Answer 7

The if here is the normal if, but the phrase, "if you want" is often a sort of implicit invitation to partake in whatever's being talked about.

The first example is essentially shorthand for something like:

I'm going to open a bottle of lemonade, (and) if you want some (you can have some).

The if is conditional, but it's not conditioning over whether or not the bottle is opened, it's conditioning over whether or not you will have any.

Another example might be, "we're going to the restaurant, if you want to come." The if has nothing to do with whether or not the speaker is going to go to the restaurant. They're saying you can come too if you want to.

You could use a comma in the second example, but it would be unnecessary. The comma in the first example is necessary because otherwise it would look too much like the first part is conditioned on the second part.

Answer 8

In terms of teaching uses in English:

will is used to offer to do something:

• If you're hot, I'll open the window.

• If you're willing,she'll do the housework now.

• I'll open a bottle of lemonade if you want some. [an offer]

• If you don't, I won't. [continuation of previous sentence]

English lessons from the British Council

Promises, offers and requests We use I will or We will to make promises and offers:

• I'll give you a lift home after the party.
• We'll come and see you next week.

This use of will is equally true in BrE and AmE. It also applies to third person if you speaking in that person's name:

• He'll finish the job now, if you agree.

The conditionality [if] of the action is dependent on the person's accepting the offer made by the speaker.

• I'm going to open a bottle of lemonade, if you want some.
• I'm not going to open a bottle of lemonade if you don't want any.

I think the negative makes the use of if in the first sentence perfectly clear. I don't see how to explain it more clearly. The action of the main clause depends on a condition the speaker of that clause assigns to the second person in the conversation. This is a standard speech usage. "I'm going to do something" + if you [verb] is a definite action, not an offer to do something for someone.

I'm going to open a bottle of lemonade, if you want some. = I am doing it and you can have some since that is what I wiil be doing.

Another example:

• I'm going to leave early tomorrow if that is what you want me to do.