11.3.1 Subject-auxiliary inversion after negative adverbials

HARDLY, SCARCELY, BARELY, NO SOONER

hardly / scarcely / barely ... when
no sooner ... than

When a story is told in the past tense, the adverbials hardly, scarcely, barely and no sooner are often used to emphasise that one event quickly followed another. The verb describing the earlier event is usually in the past perfect tense. If hardly, scarcely, barely and no sooner are in the initial position, the subject and auxiliary are inverted:

Hardly had I arrived home when my phone rang. (I had hardly arrived home when my phone rang.)

Scarcely had she finished reading when she fell asleep. (She had scarcely finished reading when she fell asleep.)

Barely had they won the match when the coach had a heart attack. (They had barely won the match when the coach had a heart attack.)

No sooner had the company launched its new product than it went bankrupt. (The company had no sooner launched its new product than it went bankrupt.)

Note that hardly, scarcely and barely are followed by when, while no sooner is followed by than. (Sooner is the comparative form of soon.)

NEVER, RARELY, LITTLE, IN / UNDER NO CIRCUMSTANCES, ON NO CONDITION, IN NO WAY, NOT ONLY ... BUT ALSO etc.

When never, rarely, little etc. are placed at the beginning of the sentence for rhetorical effect, the subject and auxiliary are inverted:

Never (before) have we faced such a challenge! (We have never faced such a challenge!)

Rarely has there been so much speculation about the future of the company. (There has rarely been so much speculation about the future of the company.)

Little did she understand what the conversation was about. (She didn't really understand what the conversation was about.)

Under no circumstances are you allowed to disturb the pilots. (You are not allowed to disturb the pilots under any circumstances.)

On no condition will the company bear responsibility for lost property. (The company will not bear responsibility for lost property on any condition.)

In no way am I related to the suspect. (I am in no way related to the suspect. )

Not only did he exceed the speed limit, but he had also consumed alcohol. (He not only exceeded the speed limit, but he had also consumed alcohol.)

Not only were you late, but you didn't even have a good excuse. (You were not only late, but you didn't have a good excuse either.)

ONLY AFTER, ONLY IF, ONLY IN THIS WAY etc., NOT UNTIL

When only after, only if, only in this way etc. are placed at the beginning of the sentence for rhetorical effect, the subject and auxiliary are inverted:

Only after lunch can you play. (You can only play after lunch.)

Only after finishing your homework can you play. (You can only play after you finish your homework.)

Only after you have finished your homework can you play. (You can only play after you have finished your homework.)

Only by guessing can you solve this puzzle. (You can only solve this puzzle by guessing.)

Only if everybody agreed would I accept this position. (I would only accept this position if everybody agreed.) 

Only in this way does this machine work. (This machine only works in this way.)

Only then did they discover his secret. (They only discovered his secret then.)

Only when he needed some help did he call me. (He only called me when he needed some help.)

Only when I filled my glass did I notice that it was broken. (I only noticed that my glass was broken when I filled it.)

The last sentence can be rephrased as:

Not until I filled my glass did I notice that it was broken. (I didn't notice that my glass was broken until I filled it.)

If only is followed by the subject at the beginning of the sentence, there is no inversion:

Only you can understand. (No one else can understand.)