If Erik phones, I'll let you know.

If Erik phones, I'm going to let you know.

Is there any difference in meaning? My grammar book says it does, but the explanation is confusing.

It says:

However, we use will, not be going to, when the main clause refers to offers, requests, promises, etc. and ability:

If Erik phones, I'll let you know. (=an offer; '..., I'm going to let you know' suggests 'I intend to let you know when Erik phones')

  1. Isn't it a promise, not an offer?
  2. I see no difference in 'I'll let you know' and 'I intend to let you know'.

Another example sentence goes like this:

If you look to your left, you'll see the lake. (=you'll be able to see; '... you're going to see... suggests 'I know this is what you can see when you look to your left').

This is not clear as well.

Please help me figure this out.

  • Your book says that will is used with 'offers, requests, promises etc.', so whether it's seen as an offer or promise makes no difference to the grammar. Nov 19, 2021 at 8:46
  • @KateBunting thank you for your reply, it's clear and I understand why we use 'will' in those example sentences, but I'm still a bit confused about 'going to' examples. 'If Erik phones, I'm going to let you know' and 'If you look to your left, you're going to see the lake', do we use 'going to' in order to stress the point that the phone call and the lake are important (special) to the speaker or the listener or what? Thanks in advance!
    – bobby
    Nov 19, 2021 at 21:40
  • The use of going to would not be idiomatic in those sentences (though, on a train journey for example, the experienced traveller might say "In another ten minutes you're going to see the lake", speaking of a treat that's in store). Nov 20, 2021 at 9:31

1 Answer 1


In sentences like this, will is used for things that will happen as a matter of course. The view of the lake is there for all to see; the person only has to turn their head. Erik's phone call probably concerns the person being addressed, so it's only natural that the speaker will pass on his message.

I'm going to is more likely to be used when someone has made up their mind to do something, or is promising something special.

When Erik phones, I'm going to tell him just what I think of him for treating you like that!

You're going to see some wonderful scenery when we get into the mountains!

  • Yes, to show determination, often with exasperation. Nov 19, 2021 at 11:13
  • @EdwinAshworth excuse me, to show determination, often with exasperation, we have to use 'going to', am I correct?
    – bobby
    Nov 19, 2021 at 21:34
  • @bobby To show determination, especially with exasperation, using 'going to', (with heavy stress on at least those two words) is a common device. 'If Erik doesn't call mum in the next few days, I'm going to give him a piece of my mind!' Nov 20, 2021 at 12:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.