Business English: A Practice Book by Rose Buhlig

3. Sometimes the pronoun refers to a word that has not been expressed or

to an _idea_. In that case, the antecedent must be supplied; as, _Wrong_: If any one wishes to contribute to the cause, let him send _it_ in the enclosed envelope. _Right_: If any one wishes to contribute to the cause, let him send _his contribution_ in the enclosed envelope. _Wrong_: I wouldn't wear mittens. Nobody does _that_ nowadays. _Right_: I wouldn't wear mittens. Nobody wears _them_ nowadays.