This is an explanation by a native speaker. It includes the notions of RHEME and THEME
The explanation
"I live in France but I usually travel abroad", sounds odd because there's no context, so we don't know what the rheme (the new information) and the theme (the already understood information in the context) is."
1
- I guess you've travelled all over France then since (= because) you live there?
- I do live in France but I usually travel abroad (the rheme or new information is that I do my travelling abroad, not in France).
2
- I've tried to phone you several times on your landline in France, but there's never any answer.
- I do live in France but I'm usually travelling abroad. (The rheme is not where I do my travelling, but what I am usually doing that makes it difficult for you to contact me on my French landline.)
Does it make sense to you? Because to me it poses more questions than answers. Apparently, the author sees a connection between a rheme and a tense. But what regulates this system that is which rheme requires which tense? I don't understand why in the first example it is "I usually travel" and in the second "I am usually travelling" and both of them have reasoning which I don't see any ground for.
Can you explain what is going on here?