Let consider that someone will take a flight tomorrow with a plan of course. In this case, we can use
He's going to fly tomorrowin Simple Future.
How ever, I’ve learnt that we can also use Present Continues to represent this situation in future too. So we’re allowed to use
He's flying tomorrow.
On other hand, I also learnt that Simple Present can be used to represent an action in future too. So
He flies tomorrowis correct too.
So my question is this:
- What is the difference between them? are they exactly same?
- When should we use which one?
They all mean the same thing but there is a bit of difference in the way that they are used.
The most general, and the most widely used, is “He’s going to fly tomorrow”. This can be used with no background, for example “My son needs a flight bag quickly, he’s going to fly tomorrow”: alhough it can also be used with background, for example “My son is going to Australia.” “Oh, when does he go?” “He’s going to fly tomorrow.”
The next most common form is “He’s flying tomorrow”. This would nearly always be used with background, for instance “My son is going to Australia.” “Oh, when does he go?” “He’s flying tomorrow”. It would be grammatically correct to use it without background (“My son needs a flight bag quickly, he’s flying tomorrow”) but might sound a bit odd because you haven’t said where he’s going.
The least common form, partly because it’s more formal and in some ways a bit dated, is “He flies tomorrow”. If you said “My son needs a flight bag quickly, he flies tomorrow.” it would be correct but would sound a bit odd and, probably, pretentious. It would be more likely to be used in more formal, significant or dramatic situations. For example “My son is going to Australia to negotiate a 500 million dollar deal, he flies tomorrow.”
If you are in any doubt use “He’s going to fly tomorrow”, I can’t think of any circumstance where it would sound wrong. The one to be most careful with is “He flies tomorrow.” as it can be inappropriate.