Let me explain what I have understood regarding this matter.
be + verbing can be used with adverbs of time to express something will happen or someone will do something in the near future. 3 ways talking about this matter. I’ll tell you what.
1- If you don’t really have an idea of when exactly you will do something in the future, just use will be + doing + adverb of time. e.g I’ll be thinking of getting married in September.
2- When you have that idea and it’s a bit more certain, just use, be + doing + adverb of time. e.g I am getting married in September.
3- When you have a detailed plan of what you will certainly do, say, you have planned for wedding at the church, reception… and you have invited you friends to your wedding… and the wedding will happen on a specific day by all means, just use be + going to do something. e.g, I am going to get married in September.
Anna, I don’t really understand your first example: “I will be thinking of getting married in September”. It means I am not yet thinking about it, but I wil start thinking in September. The date of the marriage ceremony will be even further off, could be January.
Incidentally, the verb “to get” might have complicated things a bit in your examples, because it has a somewhat ‘futurish’ flavour itself as well.
I’d make a somewhat different classification:
a.) Plain Future
He will move to London in September: plain future.
He is going to move to London in September: plain future, almost the same as “will”.
b.) Near Future
He is moving to London in September: usually near future - when it is future at all: in many contexts it is simply the continuous.
I do not think I agree with you Cerberous. “in September” is an adverb complement for “getting married”, not for “thinking of”, so I do not think it means I will not start thinking about that till September. Setember is a point of time in which my wedding cecermony if any will happen.
That’s the idea I was taught and I myself think it’s reasonable.
“I will be thinking of getting married in September”.
Okay, I guess you could take “in September” with “getting married”, though I find that less likely. Even so, the sentence would be odd. I would then paraphrase it as follows:
“At some time in the future, I will start thinking about getting married, but it is already known now that the marriage will take place in September.”
This implies that I am not yet thinking about it now: otherwise, I would not say “will be thinking” but “am thinking”.
It seems very odd, having a date for the ceremony while not even having thought of marriage, while not even having decided whether I will get married at all. You see how I would interpret your sentence? Perhaps one of the experts on this forum should have a look at this.
As I said, I would rephrase it into “I am thinking of getting married in September”. The “getting married” must be in the future anyway, because it must happen after the thinking, which happens now.
The way that sentence is written says that the thinking will take place in September. Thus, it should say “I’m thinking of getting married in September.”