The poet, the dramatist, the novelist are free to exercise their imagination as widely as they choose. But the historian may not be allowed so long a tether. He must fulfill his function as creative artist only within very rigid limits. He cannot invent what went on in the mind of St. Thomas of Canterbury. The poet can. He cannot suppress inconvenient minor characters and invent others who more significantly underline the significance of his theme. The novelist can. The dramatist can. The historian, as Sir Phillip Sydney has said, "is captive to the truth of a foolish world." Not only is he captive to the truth of a foolish world, but he is captive to a truth he can never fully discover, and yet he is forbidden by his conscience and his training from inventing it.