I've been going over Advanced Grammar in Use and came across Unit 9 Rule E I'll cite a part of it:

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

There are two examples the first of which I'll omit.

If you look to your left, you will see the lake.

= you will be able to see, you are going to see suggests: "I know this is what you can see when you look to your left"

The question is not about the rule itself but rather about the explanation about the difference between the usage of will/be going to here. I don't quite understand what they mean by saying "I know this is what you see.." Is it just about letting them know that you have already seen that or what?

I would like to ask to clarify this "be going to usage" and tell me a real life situation where this might be useful, in other words another example, thanks!

  • I don't think your "rule" is accurate, for example as a promise: "I will get you your money by tomorrow" and "I am going to get you your money by tomorrow" are both fine. Similarly "Will you get us coffee on your way home?" and "Are you going to get us coffee on your way home?" are both grammatical, although the first is more a request and the second more an expectation.
    – Andrew
    Jun 28, 2017 at 19:48
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    It's very important to understand that most of what you will read in Hewings's Advanced Grammar in Use and similar reference and practice books, such as Swan's, are not rules. A rule is, for example, "The verb must agree in number with its subject: write He walks, not He walk." Hewings's book and the others aren't rule books; they are compilations of usages with examples and explanations designed to help you learn to speak, write, and understand English. Jun 28, 2017 at 20:04
  • Well, they contain a lot of rules just it's the advanced level so they mostly explain the shades of meaning and sometimes there are rules that you must follow. But in broad terms I understand what you are trying to say and yes I understand it , thanks! And it's not "my" rule , I told where it is from :)
    – Dmitrii
    Jun 28, 2017 at 21:00
  • As for: "I will get you your money by tomorrow" I think suggests that you will certainly give this money back, you promise it. But in "be going to" it is your intention and it is more about "maybe". The rule doesn't tell you that it is prohibited to use "be going to" it says that IF you promise/offer/etc you have to use will.
    – Dmitrii
    Jun 28, 2017 at 21:11
  • @Dmitri Both "I will get you the money" and "I'm going to get you the money" mean much the same thing. Your interpretation depends far more on whether you trust me, and not which expression I use. Both can be interpreted as a "promise" -- if you believe that I keep my promises.
    – Andrew
    Jun 28, 2017 at 21:24

1 Answer 1


If you look to your left, you will see a hippopotamus.

If you look to your left, you are going to see a hippopotamus.

The speaker knows about the hippopotamus in either case, and so to express the difference between the two in terms of the speaker's knowledge is confusing and not very illuminating. We might express the difference in terms of the speaker's foreknowledge.

will refers to a predicted outcome.

are going to refers to a predicted eventual outcome.

If you eat this poison mushroom, you will regret it.

If you eat this poison mushroom, you are going to regret it.


If you look to your left, you will see a hippopotamus.

If you look to your left, you are going to see a hippopotamus. It will be visible momentarily.

  • Hm, that's interesting , I would like to know the meaning of your "eventual" term. What is "eventual outcome" compared to "regular outcome"? I don't understand this "foreknowledge thing" , in both cases we know that they will be there when we look to the left.What does"It will be visible momentarily" have to do with that?
    – Dmitrii
    Jun 28, 2017 at 21:07
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    @Dmitrii Momentarily (as we use it in American English) means in a moment. Tᴚoɯɐuo is saying that the speaker knows this, and that by saying "you are going to see a hippopotamus", the speaker communicates that the hippo will appear a moment after you look to your left. Jun 28, 2017 at 21:15
  • And if you say "you will see a hippopotamus" what will it mean? Just stating the fact that there is one? And how could they be compared from this "time" perspective?
    – Dmitrii
    Jun 28, 2017 at 21:42
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    @Tᴚoɯɐuo Thing is, Hewings doesn't really treat this distinction in this section of AGIU (or anywhere afaict) so the OP is winging it here. The word foreknowledge appears nowhere in the book. :( Jun 28, 2017 at 22:01
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    @Dmitrii: These two questions are conceptually related: What is the difference between outcome and eventual outcome, and between knowledge and foreknowledge. However, these questions are not about English per se but about epistemology. What I would like you do is to is to visit a couple of good dictionaries (not learners dictionaries), consult the definitions of those two words, and then tell me what it is about the definitions that fails to clarify the issue for you. At that point I would be happy to append a P.S. to my answer where I will try to address the issue.
    – TimR
    Jun 29, 2017 at 18:00

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