Rule: A pronoun object that is co-referential with the subject of the clause in which it occurs must be reflexive.
Example of error:
(1) The application of technology to entertainment gives us more chances to entertain us in an active way than our ancestors ever had before.
The reflexive pronouns are myself, yourself, himself. herself. itself. ourselves, themselves. The subject of the clause in which the reflexive pronoun occurs need not be the subject of the sentence, as (1) illustrates. The clause in which us (i.e. ourselves) occurs is infinitive (to entertain) and functions as a postmodifier of chances. This infinitive clause, however, is the clause in which the reflexive pronoun ourselves must occur, since the pronoun is co-referential with the subject (we) of the infinitive--even though in this case the subject remains unexpressed.