When to use no sooner and as soon as in English grammar?

Answer 1

These two phrases have overlapping meanings but are not exactly synonymous. No sooner ... than can generally be replaced by as soon as, but as soon as cannot always be replaced by no sooner ... than.

No sooner is always followed by than and emphasises that one thing happened immediately after another. It is normally used in the past tense. For example:

'No sooner had I finished my meal than the doorbell rang.'

'No sooner did it stop raining than I found my umbrella.'

(Note that the subject/verb order in the no sooner ...clause must be reversed: 'had I finished', not 'I had finished'; 'did it stop', not 'it stopped'.)

As soon as can be used instead, but it is less emphatic than no sooner ... than:

'As soon as I had finished my meal, the doorbell rang.'

'As soon as it stopped raining, I found my umbrella.'

As soon as can also be used with the present and future tenses, unlike no sooner ... than:

'As soon as it stops raining, I'll go to the shops.'

'He will send you the book as soon as you send him the money.'