Does the main clause determine everything?

If the clause is If I disturbed you:

1. If I disturbed you, I am sorry.
2. If I disturbed you, I would give you money.

Both of them use the past tense of disturb in the 'if-clause'

According to the subjunctive mood of past, 2 means 'As I don't disturb you, I will not give you money' (assuming the opposite of the present fact or situation: past subjunctive).

According to the indicative mood, 1 means 'I disturbed you in the past and I am sorry now.'

1 and 2 use same if clause using the same disturbed (literally the same if-clause) but has two different meanings due to different main clauses (I am sorry and I would give you money).

How do you know if a speaker says 'if-clause' with the intention of indicative or subjunctive. Do I have to wait for the main clause that follows the 'if-clause'?

If so, does the main clause determine the mood of the 'if clause'? (An important fact is that "a speaker opens his mouth and says exactly the same sound/thing").

Solution 1:

Distinguish Real vs Unreal,
not Indicative vs Subjunctive

English conditional clauses like these should not be classed as “subjunctive” vs “indicative” because English doesn’t really have “moods” in any inflectional or morphological sense of that term.

Instead of moods, what English does have is modals, which with one unique exception, are what we must use whenever something is other than real. And your reals always come in exactly one of English’s two inflectional tenses, either past or present.

It is convenient to group conditionals by the nature of the verbs in their consequent clauses, which can therefore be exactly one of either real or unreal. All modals are by definition unreals.

1. If I disturbed^{real (past)} you, I am^{real (present)} sorry.
2. If I disturbed^{real (past)} you, I would^{unreal (modal)} give you money.

In both your two cases, the if parts use a real verb: disturbed. It is not “subjunctive”. The reality or lack of same is indeed indeterminate until you get to the then part. At that point, the first is real and the second is unreal.

There are various other possibilities, including those with other reals and other modals alike. Remember that to make something unreal, you always need a modal (or singular were).

4. If I disturb^{real (present)} her, she always becomes^{real (present)} upset.
5. If I disturbed^{real (past)} her, she always became^{real (past)} upset.
6. If I disturbed^{real (past)} her, she would^{unreal (modal)} always become upset.
7. If I can^{unreal (modal)} disturb her, she may^{unreal (modal)} wake up.
8. If I were^{unreal (were)} to disturb her, she might^{unreal (modal)} become upset.
9. If she need^{unreal (modal)} not be disturbed, I will^{unreal (modal)} leave her in peace.

Here’s a bit of background on this classification system. It works out much better than imagining things that English does not even have.

1. Reals

Real presents

These are actually “non-pasts”, but most people call them presents.

Except for be, these have a special inflection in only the third-person singular alone and nowhere else.

• She disturbs me.
• I disturb them.
• I am disturbed.
• You have got to be kidding!
• He has disturbed you.
• It has been stopped.

Real pasts

These are inflect for the past tense, with all persons and numbers the same except for be.

• I disturbed her.
• They disturbed me.
• He did disturb her.
• It had been stopped.
• She was disturbed.
• I was going to disturb her.
• They were disturbed.

2. Unreals

All unreals are modal unreals except sometimes for be.

Unreals via modals

These always use one of the standard English modals plus an uninflected lexical verb following.

Additionally, there are three pairings of modals that for backshifting purposes pair a “present/non-past” version coupled with a “past” version: will/would, shall/should, and may/might.

• I can^modal disturb her.
• Shall^modal I disturb her?
• He could^modal disturb her.
• You should^modal not disturb her.
• I may^modal disturb her.
• I will^modal disturb her.
• I would^modal disturb her.
• They might^modal have disturbed.
• Dare^modal he disturb you?
• One need^modal not disturb them.
• Oughtn’t^modal you not disturb her now?

The zero modal

One other modal verb that comes into play with these uninflected lexicals is the so-called “zero-modal”. It isn’t an actual word, but we can construe its existence here because it modally marks the verb following in the very same way that a written-out modal does.

This type of modal is found only in special clause types.

• They are insisting that I ^zero-modal be there early.
• They were insisting that I ^zero-modal be there early.
• God ^zero-modal bless you.
• Long ^zero-modal live the king.
• ^zero-modal Have a nice day.

Being modals albeit of the zero variety, these are all still necessarily unreals. That’s because all modals are always unreals.

Unreals via were

This occurs only with unreal were, normally the real plural past of be. It is therefore morphologically distinct from the real past plural only when it takes a singular subject.

• Imagine it were^{unreal (were)} so.
• He acted as if she were^{unreal (were)} here.
• If only she were^{unreal (were)} here.
• I wish this were^{unreal (were)} easier.
• She would have left us a note if she were^{unreal (were)} ready to leave.
• Unless she were^{unreal (were)} ready, she would leave us no note.