1.10.8 Omission of relative pronoun

Rule: The relative pronoun cannot be omitted in a non-restrictive relative clause.

Examples of errors:

(1) These outsiders live in a sort of subculture-they created for themselves--at weekends.

(2) Thank you for your nice letter, I received yesterday.

(3) I met lots of English people during the Lent term of 1978 I spent at the University of Reading.

Relative pronouns may be omitted from restrictive relative clauses, so long as they are not the subject of the clause; compare:

Thanks for the nice letter (that) you wrote me.

This is the letter-that contains my resignation.

This is not possible with non-restrictive relative clauses, however.