If/whether in indirect yes/no questions

1. When if or whether is needed

A direct yes/no question, without a question word such as what, where, or why, cannot simply be inserted into another sentence. English needs a linking word to mark the beginning of the indirect question. If and whether perform this role.

This distinguishes yes/no questions from questions with their own question word. In those, what, where, or why already introduces the embedded question, so an additional if or whether is unnecessary.

You need this link when reporting a yes/no question, asking about a yes/no fact indirectly, or expressing uncertainty about one: I wonder if…, Do you know whether…, She asked if….

How to build it

main frame (know / wonder / ask / tell me / not sure ...) + if / whether + subject + verb

subject / S: The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.
verb / V: A word for an action or state, such as work or be. The pattern determines its form.

Do you know if the library is open this Sunday?

The direct question would be Is the library open? It has no question word, so if is needed in this version.

I wonder whether the airport bus runs on public holidays.

Whether works in the same way as if here.

2. If and whether are mostly interchangeable

In ordinary embedded yes/no questions, the two linking words are often interchangeable without changing the meaning.

The British Council notes that if is more frequent, especially in conversation. Whether is neither outdated nor incorrect; it is another, slightly more formal option for the same question.

Next, we examine positions where whether is required or is the better neutral choice, and cases where if can be ambiguous with a conditional meaning.

She asked if the dentist could see her today.

Whether the dentist could see her today would be equally correct here, with the same meaning.

Could you find out whether the parcel needs a signature?

Whether can also be replaced by if here without any loss of meaning.

3. Only whether before a to-infinitive

When the indirect question uses to + verb, such as to accept, to go, or to book, only whether can introduce it. If is not used in this position.

The standard indirect-question pattern with a to-infinitive is whether to do something. If to do something is not the corresponding pattern.

How to build it

whether + to + base verb

verb / V: A word for an action or state, such as work or be. The pattern determines its form.
V1 / base form: The base verb without to: work, go, be.

I haven't worked out whether to book the earlier train.

If to book is not possible here.

They're still discussing whether to move the office to a bigger building.

The same pattern: whether directly before to.

4. Whether after a preposition and as the subject

After a preposition in these standard patterns, use whether: discussion about whether…, depends on whether…. This is a reliable choice for neutral and formal writing.

When the question clause itself is the subject at the beginning of the sentence, whether is required: Whether we go depends on the weather. Whether is also usual in a complement after be, although the conversational The question is if we can afford it is possible; that is a different position.

How to build it

preposition + whether ...; Whether ... + main-clause predicate

clause: A construction with a verb, often with its own subject: when I arrived. A non-finite clause may leave the subject unspoken: to get home.
preposition: A word showing a relationship, such as in, on or from: from Ukraine.

There was a lot of discussion about whether the bridge needed repairing.

Whether is natural after about here, especially in neutral or formal writing.

Whether the garden party goes ahead depends entirely on the weather.

Whether introduces the subject of the whole sentence: whether the garden party goes ahead is what depends on the weather.

5. Whether or not: where or not goes

Whether can come immediately before or not: whether or not + subject + verb.

If does not work this way. With if, add or not at the end of the clause, after the complete subject and predicate, not directly after the linking word.

How to build it

whether or not + ...; ... if + ... + or not

I'm going to the concert whether or not it rains.

Here whether or not means regardless of whether: this is a concessive construction, not an embedded question. For an actual embedded question, compare I don't know whether or not it will rain, which expresses uncertainty about rain.

I don't know if the shop takes cards or not.

With if, or not goes at the end; it cannot come immediately after if.

6. Word order inside the indirect question

After if or whether, the indirect question follows statement word order: the subject comes before the verb.

Remove do, does, or did used only to form a neutral affirmative question; the main verb then expresses tense and agreement. Negative doesn't/didn't and emphatic do can remain: I wonder if he doesn't like it; I wonder if he did call.

How to build it

if/whether + subject + predicate (statement word order)

subject / S: The grammatical subject: who or what the clause is about; the verb agrees with it. In The book was written, the book is the subject, although someone else does the action.

Can you check if the printer has enough paper?

Has follows the subject directly, without auxiliary does.

She asked whether the neighbours had heard the noise last night.

Use had heard after the subject, not the inverted had the neighbours heard.

7. Final punctuation depends on the main clause

The if/whether clause is not a separate question; it is part of a larger sentence. The final full stop or question mark therefore depends on the MAIN clause, not merely on the presence of a question within it.

If the main clause itself asks someone a question, as in Do you know…? or Could you tell me…?, end the whole sentence with a question mark. If it makes a statement or expresses a thought, as in I wonder… or I'm not sure…, use a full stop.

I wonder if the dentist has any appointments free tomorrow.

I wonder is a statement, so use a full stop even though it contains an embedded question.

Do you happen to know if the dentist has any appointments free tomorrow?

Do you know…? is a question addressed to the listener, so use a question mark.

8. Register: conversational if, more formal whether

This is a tendency, not a strict prohibition: if occurs more often in relaxed conversation, while whether is common in official correspondence, reports, and academic writing.

When both forms are grammatical, also consider meaning: if can be interpreted as conditional. Let me know if you are coming can sometimes mean tell me only if you will come, while whether more clearly requests either of the two answers.

Let me know if you fancy grabbing a coffee later.

The tone is relaxed, and if sounds natural.

We would appreciate confirmation of whether the delivery date can be moved forward.

After of, whether is the neutral formal choice; this is not just about the overall tone of business correspondence.

Common mistakes

Incorrect:Do you know if is the chemist's open until nine?

Correct:Do you know if the chemist's open until nine?

After if, the subject must precede the verb as in a statement, rather than follow it.

Incorrect:He asked me if did I like the presentation.

Correct:He asked me if I liked the presentation.

There is no inversion in this neutral reported question: if I liked. Did can occur in other embedded questions for emphasis, but then it follows the subject.

Incorrect:We haven't agreed if to change the schedule.

Correct:We haven't agreed whether to change the schedule.

Only whether is possible before the infinitive to change; if is ungrammatical here.

Incorrect:There's some uncertainty about whether are the results accurate.

Correct:There's some uncertainty about whether the results are accurate.

After whether, use statement order the results are, without question inversion.

Incorrect:I can't say if or not the offer is genuine.

Correct:I can't say whether or not the offer is genuine.

Only whether can immediately precede or not. With if, move or not to the end of the clause.

Incorrect:If the plan succeeds is anyone's guess.

Correct:Whether the plan succeeds is anyone's guess.

When the clause itself is the sentence's subject, use whether, not if.

Incorrect:I wonder if the tour starts at ten?

Correct:I wonder if the tour starts at ten.

I wonder is a statement, so it takes a full stop even when it contains an embedded question.

Incorrect:Can you tell me if whether the gallery has reopened?

Correct:Can you tell me if the gallery has reopened?

Use only one linking word, if or whether, never both together.

Sources