Is this sentence grammatically correct:
Is it twice as much, (then) we call it 2 G.
with or without the "then"?
In a comment thread on another SE site I was corrected on a detail as a grammatical error. The sentence should rather be:
If it is twice as much, (then) we call it 2 G.
The point apparently is that starting a sentence with "Is" (or "Are") requires a question mark at the end - which I don't have, since the sentence answers itself.
I am not native English but was very surprised by this correction. I tend to use that structure often to shorten a sentence as much as possible.
So, I'd like a second view on this from the English SE site to be 100 % convinced. Is the sentence structure "Is it ..., then ..." incorrect and should rather be "If it is ..., then ..."?