later than that of his prophetic activity. It is usual in biblical study to refer to passages that do go back to the prophet as ‘authentic’ or ‘genuine’, and to those that do not as ‘inauthentic’ or ‘secondary’. As we shall see, these terms must not be taken as expressing value judgments, only historical hypotheses about who wrote which parts of the prophetic books. But in none of the prophets is the question of ‘authenticity’ so difficult as in Isaiah. Scholars have spent a great deal of time—some