Even the usually conservative/traditional Roman Catholic church has agreed with modern scholarship that there are several different persons responsible for the content of the book of Isaiah. http://www.usccb.org/bible/isaiah/0. read more
then the book of Isaiah was dissected further, so that one scholar ascribes Isaiah chapters 15 and 16 to an unknown prophet, while another questions the writership of Isaiah chapters 23 to 27 still another says that Isaiah could not have penned the words found in Isaiah chapters 34 and 35. read more
The one consensus is that Isaiah 40-55 was not written by the same person who wrote Isaiah 1-39. Jake Stromberg says, in An Introduction to the Study of Isaiah (2011), that scholars in the current century acknowledge that the Book of Isaiah must have had multiple authors, the view is moving towards seeing interdependence between chapters 1–39 and 40–66. read more
While one part of the consensus still holds – virtually no contemporary scholar maintains that the entire book, or even most of it, was written by one person – this perception of Isaiah as made up of three rather distinct sections underwent a radical challenge in the last quarter of the 20th century. read more