8.108 USAGE NOTE

Other expressions can be used in defining clauses in place of 'when', 'where', 'why', and 'whereby'.

After 'time' you can use 'at which' instead of 'when'.

After 'place' and words such as 'room', 'street', 'year', and 'month', you can use 'in which' instead of 'where' or 'when'.

After 'day' you can use 'on which' instead of 'when'.

After 'reason' you can use 'that' or no pronoun instead of 'why'.

After words such as 'situation', 'stage', 'arrangement' or 'system' you can use 'in which' instead of 'where' or 'whereby'.