I've promised that I will (sequence of tenses)

[angelene001]

Which sentence is correct:
1. I've promised that I will help her
or
2. I've promised that I would help her

When we apply rules of the sequence of tenses how do we treat Present Perfect?

[5jj]

When we apply rules of the sequence of tenses how do we treat Present Perfect?

As a present tense.

I've promised that I will help her.
I promised that I would help her.

I promised that I will help her is also possible if the help is seen as future to the time of the reporting.

[Chicken Sandwich]

I promised that I will help her is also possible if the help is seen as future to the time of the reporting.

5jj, I don't follow you here. I've always thought that "promised" (or rather the past tense of a verb) and "will" don't go together*, like you did here. Let's take an example:

A teenager who's going to a concert says to his mother:
Mum, I promise that I will go straight home after the concert.

At the concert. The teenager says to his friend.
Sorry, I can't hang around. I promised Mum I'd go straight home after the concert.

I'm not sure how to use "promised" in conjunction with "will". Are you saying that I could use "will" here instead of "would? Or how would you use it here?

Thank you in advance.

*Common Mistakes at Proficiency by Julie Moore says on p. 5 that it's a common mistake.

[5jj]

5jj, I don't follow you here.

Ms Moore thinks it's a mistake. I don't. Nor do Professors Quirk et al (A Contemporary Grammar of the English Language), Leech (Meaning and the English Verb), Huddleston and Pullum (The Cambridge Grammar of the English Verb) and others on my bookshelves.

You may backshift all the time. That's fine; I have no objection; it's correct. I, however, can say, "I promised my mother that I'll (or: I'd) go straight home after the concert" if it is still true that I will go straight home after the concert. Both forms are correct.

If, when I say those words, I have no intention of keeping the promise, or it is already past the time of going straight home, then I can use only "I'd".

[Barb_D]

A: Sandy really needs help. I'm surprised she hasn't asked you to help her.
B: I've already promised that I will help her, but I need to take care of something else first.

There is no need for her to ask me - I've already made the promise. Connection to the present.

[5jj]

Some teachers, and even some course books and students' grammars seem to think that the fiction that backshifting after a past-tense verb of speech is impossible is helpful for learners - like the untrue claims that verbs of emotion (love, hate, etc) cannot be used in progressive forms, or that will can never be used in if- clauses. I don't.

It is true that backshifting is (almost) always correct. That, however does not mean that absence of backshifting is always wrong.

[Chicken Sandwich]

You may backshift all the time. That's fine; I have no objection; it's correct. I, however, can say, "I promised my mother that I'll (or: I'd) go straight home after the concert" if it is still true that I will go straight home after the concert. Both forms are correct.

Yes, that is the situation I was talking about. Interesting. This is certainly new to me.

Here's the full quote from the book I was referring to:

1 Tick he correct sentence in each pair.
[...]
2 a I promised Mum I'd go straight home after the concert.
b. I promised Mum I'll go straight home after the concert.
[...]

The key indicates that a is the correct answer here (rendering b incorrect).

We also use would to talk about a time in the future from a point in the past:
They planned that they would meet at midnight.

My reasoning wasn't actually based on this book. I still do not understand how "will" can be justified in sentence 2b even if, as you say, it is till true that I will go straight home to the concert. The promising happened in the past, so "would" seemed like the most likely option. "will" seemed only possible if the promising is happening now as in 'I promise that I will go straight home after the concert'.

But I will look into it, since you say that this is a common myth.