References in classic literature ?
The occurrence of the content of a thought constitutes the occurrence of the thought.
Speaking in popular and unphilosophical terms, we may say that the content of a thought is supposed to be something in your head when you think the thought, while the object is usually something in the outer world.
Realists, on the other hand, as a rule, suppress the content, and maintain that a thought consists either of act and object alone, or of object alone.