Should I need to use an 'a' before 'sound sleep' in this sentence ?
''He was in sound sleep''
Regards
Should I need to use an 'a' before 'sound sleep' in this sentence ?
''He was in sound sleep''
Regards
These Google Ngrams seem to show that 'was in sound sleep' is used, though not as often as 'in a sound sleep' (though there may be various false positives). But 'was soundly asleep' seems the most idiomatic variant, which is as I imagined.
There are various non-count (* He was in two sound sleeps that weekend) expressions favouring/requiring the inclusion of the indefinite article.
He was in a daze / a coma; this puts it in a different light; she has a working knowledge of Urdu....
Sometimes, inclusion is optional.
The director spoke at the meeting today with [a] great enthusiasm.
The use of the indefinite article with non-count-noun usages has been addressed on ELU at A blinding light / blinding sunlight / a blinding sunlight?.
sound used here is an adjective that refers to deep and undisturbed. You should use a before sound sleep to make it more meaningful.
Here is an example from Oxford dictionary, His eyes closed gently, as if he was in a sound sleep, his long eyelashes clinging to one another.1