I have seen this construction quite often:
Online ads have been around since the dawn of the Web, but only in
recent years have they become the rapturous life dream of Silicon
Valley.
What is the rule there?. When your sentence doesn't start with pronoun + verb, invert them as verb + pronoun?. I know it sounds awkward but is it possible (grammatically correct) to use something similar to:
Online ads have been around since the dawn of the Web, but only in
recent years they have become…
And in any case, does this only work with have (or has)? Maybe it works fine with 'had' but I can't think of an example right now.
Best Answer
Switching around the normal word order is called inversion, and this specific type is called subject-auxiliary inversion. Wikipedia has a list of usages of subject-auxiliary inversion, including interrogative constructions (e.g. Did you eat?), but the following is the declarative section:
I found a blog called Practice English which has a laudably comprehensive post on the topic of inversion:
This is only the first 15% or so. Though not the highest quality of writing (it contains a few typos, etc), IMO it represents the contexts of proper inversion admirably well and staggeringly comprehensively.
The only real (albeit minor) disagreement I have seen that I have with it involves the following:
As far as I have seen, it's not necessarily formal to say in came the doctor - in fact, the doctor came in seems more consistent with a formal context. (It also could be that the author meant to say less informally, and if so, I'd have agreed completely).