I've been reading through Isaiah, and I've just started the second half of the book (chs.40-66). Contemporary scholarship generally assumes these chapters are not written by the 8th century prophet Isaiah, despite the book's seeming attribution of the book to him. The main reason is that they seem to be about a time much later, the return from exile in the 6th century. Stylistic considerations are also cited, but this turns out to be a bit of ad hoc special pleading, since the same stylistic features are present throughout the first half of the book, and these scholars then pull themselves up on their own bootstraps by insisting that those earlier chapters must also be later additions. At some points this gets even as ridiculous as to minimize the contributions of Isaiah to only a very small component of the overall material even of chapters 1-35. It's taken rather to be the additions of this great school Isaiah must have founded, and thus it gets attached to his book because it's in the Isaianic prophetic school. All this makes me wonder what was so great about Isaiah to have merited this great school attributing all these great prophecies to him if what he actually did was only this tiny amount of material, none of it resembling in content most of the stuff that somehow ended up getting attributed to him.
Suffice it to say that I'm not even close to convinced that Isaiah did not write these chapters. He may not have delivered them as addresses, as he did the earlier chapters in the book, but the argument that he couldn't have written the second half of the book doesn't leave me very convinced, which leaves me taking the text's claim as the most important evidence available, and all the text does is introduce the book as the prophecy of Isaiah, with no new introduction of a new unit with other author information once you hit this second major section.
As I was reading chapter 42 this morning, something occurred to me that I hadn't thought of before.