Learn English – Usage of ‘do’ and ‘does’

First off, phrases like this September are almost always used to indicate something in the future. The original sentence is speculating about a possible future event. To refer to some September that is in the past, you would say this past September or last September.

Since this September refers to the future, it is not appropriate to use the phrase must be. Must is usually used to talk about the past, as in “The plane must have landed by now”. It can also be used to make an a guess about the present, as in “You must be joking”, or to define a rule of some sort, as in “The toys must be put away before snack time”. The only appropriate use of the word must in talking about the future that I can think of is something like “They simply MUST release a new phone this September, or I will be very angry!” But there is no be-verb associated with must in this case, so it’s different than what you’re talking about.

So, to use must be in this sentence, you would have to either be making a guess about the current release of the phone (“They must be releasing the phone right now, if only I could watch the announcement!”) or talking about the past (“There must have been a new smartphone released last September”). That last sentence sounds a little awkward to my ears, though. The better phrasing would be “They must have released a new smartphone last September”.

Your last sentence is not correct because you:

1. Used must be to talk about the past (be is present tense)
2. Used two different be-verbs (be and been) to talk about the smartphone.
3. Used this September to talk about the past

Hope this helps!

To be correct, "How is he travelling ..." should be re-ordered to "How he is travelling ..." in this situation. It is then equally as correct as "How he travels..."

"How does he travel..." is wrong in this situation, as "how" is being used as a conjunction between the two clauses. The sentence could equally be written as "It is entirely up to him how he travels." This re-ordering of the sentence makes it clearer that "how" is being used as a conjunction.

How can also used to ask a question, e.g. "How does he do it?" or "How does he travel?". Whenever "how" is being used to ask a question, it is acting like the "Wh-" words - what, when, where, why, who.

As Rudyard Kipling once wrote:

I KEEP six honest serving-men
(They taught me all I knew);
Their names are What and Why and When
And How and Where and Who.