He’ll be 20 years old tomorrow./He’s going to be 20 years old tomorrow.

[diamondcutter]

1. He’s going to be 20 years old tomorrow.

2. He’ll be 20 years old tomorrow.

(made by me)

I wonder if both sentences are correct.

 

[diamondcutter]

What about these two sentences? Are they both correct too?

1. He’s going to be 20 next year.

2. He’ll be 20 next year.

(also made by me)

 

[emsr2d2]

Yes, they are both correct. They are exactly what Piscean was suggesting when he said that he would omit "years old".

 

[diamondcutter]

Yes, they are both correct. They are exactly what Piscean was suggesting when he said that he would omit "years old".

Do you mean the sentences in #3 are both correct too?

 

[diamondcutter]

One of my grammar books says ‘will’ could be used to talk about a definite fact while ‘going to’ structure couldn’t be.
Oil will float on water.√
Oil is going to float on water.×

I think ‘he’ll be 20 years old tomorrow’ also expresses a definite fact and according to the point of view above, ‘going to’ structure couldn’t be used to replace ‘will’ in this sentence.

That is to say:
He’s going to be 20 years old tomorrow.√
He’ll be 20 years old tomorrow. ×

Maybe the book is wrong or maybe my understanding is not correct. It’s pity that I don’t remember which book it is.

I’d like to read your comments

 

[J&K Tutoring]

English has far more words than Chinese. One advantage of having so many words is the ability to express small differences without having to add extra words to a sentence.

'Going to' expresses a willingness; a plan; a desire; a prediction. I'm going to try harder next time. I'm going to take a chemistry course next semester. I'm going to have pizza for dinner. It's going to take a lot of work to get this project finished.

As such, "He's going to be 20 years old tomorrow" is not wrong, but it really doesn't fit any of the above. Turning 20 has nothing to do with whether he is willing or not (he doesn't plan to be 20, he will be 20 whether he is willing or not). We might say we predict he will be 20, but that's too easy to be meaningful, so "He's going to be 20 tomorrow" isn't the best way to express that idea.

 

[Rover_KE]

One of my grammar books ...

Always tell us the title and author of any book you quote from, please.

 

[GoesStation]

"He's going to be 20 tomorrow" isn't the best way to express that idea.

But it's a very common way to say it.

 

[Skrej]

We also use the 'going to' form when there is evidence or signs to indicate something's likely to happen. Sometimes this is expressed as predictions based on evidence, as opposed to predictions based on opinion (will).

So, unless something unexpected like death happens before midnight tonight, he's going to be 20 tomorrow.

With predictions in particular, there's a lot of overlap between using 'will' or 'going to'

You can also look at a dozen different sources, and not find 100% agreement on usage of 'will' vs. 'going to' because it's not always easy to neatly pigeonhole the situation into one category or the other.

I think I'd actually be more likely to use the 'going to' form for the 20th birthday example, but both are so natural I doubt I'd even notice which version somebody else used to express the idea.

 

[jutfrank]

I think ‘he’ll be 20 years old tomorrow’ also expresses a definite fact and according to the point of view above, ‘going to’ structure couldn’t be used to replace ‘will’ in this sentence.

No, that is not what the writer means by 'definite fact'. The example Oil will float on water is an example of the use of will to make a statement of expectation. You might think of this sentence as more of a generalisation about what tends always to happen than a statement about a specific future event, as is the example about the birthday.

That is to say:
He’s going to be 20 years old tomorrow.√
He’ll be 20 years old tomorrow. ×

Because of what I said above, the reasoning here is not right. Both sentences above are possible.

Maybe the book is wrong or maybe my understanding is not correct. It’s pity that I don’t remember which book it is.

You misunderstood what the writer meant. This may have been due to the rather vague term 'definite fact'. Are you sure the writer used that term or did you make it up?

 

[Tarheel]

You could say:

He'll turn twenty tomorrow.

 

[jutfrank]

You can also avoid using modality and aspect altogether by saying:

He turns 20 tomorrow.
He's 20 tomorrow.