Although I think I could theologically live with the currently popular suggestion that the book of Isaiah was composed by at least three different sources, I find the reasons for thinking so very weak and often the reasons beg a more seminal question (about Josiah’s reform and by extension the entire standard documentary hypothesis).
Generally the breakdown between proto-Isaiah, Deutero-Isaiah, and Trito-Isaiah works as follows: chapters 1-39 belong to the first Isaiah, “the prophet of judgement”, whereas chapters 40-55 are the work of second Isaiah (Deutero), and finally chapters 56-66 are third Isaiah. First-Isaiah is generally assumed to be the real Isaiah in the eighth century B.C. and who depicts God in henotheistic fashion. Second-Isaiah is thought to be from the sixth century, and is recognized sometimes as being the inventor of Monotheism! Third-Isaiah is thought to be as late as 400 B.C. as thus clearly writing from a post-exilic perspective.
First of all, all of the arguments for thinking that this division of authorship is well supported are themselves not based on any manuscript evidence (Even the two copies of Isaiah among the Dead Sea Scrolls do not evidence any break at these chapters, even though Qumran scrolls demonstrate something like that for the book of Jeremiah), nor on any historical evidence (no historical witness exists to this effect anywhere in the ancient world) but rather on tentative arguments from form-criticism and historical-criticism. The style, in other words, is thought to be just too ‘different’ from one section to another. For example first Isaiah focuses his hope on the Davidic King (Isaiah 9:5-7, 11:1-12 etc) whereas second Isaiah focuses his hope on the suffering servant (Isaiah 52:13-53:12). First Isaiah may have been able to predict the coming Babylonian captivity, but second-Isaiah seems to have written from within a context of that captivity.
The Catholic Encyclopedia, in its article on the prophet Isaias, says:
This is hardly the place for a discussion of so intricate a question. We therefore limit ourselves to stating the position of Catholic scholarship on this point. This is clearly set out in the decision issued by the Pontifical Biblical Commission, 28 June, 1908. (1) Admitting the existence of true prophecy; (2) There is no reason why “Isaias and the other Prophets should utter propheciesconcerning only those things which were about to take place immediately or after a short space of time” and not “things that should be fulfilled after many ages”. (3) Nor does anything postulate that the Prophets should “always address as their hearers, not those who belonged to the future, but only those who were present and contemporary, so that they could be understood by them”. Therefore it cannot be asserted that “the second part of the Book of Isaias (xl-lxvi), in which the Prophet addresses as one living amongst them, not the Jews who were the contemporaries of Isaias, but the Jews mourning in the Exile of Babylon, cannot have for its author Isaias himself, who was dead long before, but must be attributed to some unknown Prophet living among the exiles”. In other words, although the author of Isaias xl-lxvi does speak from the point of view of the Babylonian Captivity, yet this is no proof that he must have lived and written in those times. (4) “The philological argument from language and style against the identity of the author of the Book of Isaias is not to be considered weighty enough to compel a man ofjudgment, familiar with Hebrew and criticism, to acknowledge in the same book a plurality of authors”. Differences of language and style between the parts of the book are neither denied nor underrated; it is asserted only that such as they appear, they do not compel one to admit the plurality of authors. (5) “There are no solid arguments to the fore, even taken cumulatively, toprove that the book of Isaias is to be attributed not to Isaias himself alone, but to two or rather to many authors”.
~Catholic Encyclopedia, Isaias
Also, the Archaeological study Bible, NIV, makes the following points against the multiple-authorship thesis.
- An author’s style depends upon a variety of factors (age, purpose, subject matter, audience, etc.), and stylistic factors like vocabulary are apt to change.
- The three “Isaiahs” do share many phrases and words, suggesting stylistic unity. For example, God is called the “Holy One of Israel” throughout (e.g., 10:17; 41:14; 60:9).
- The alleged differences are artificial. Isaiah is a lengthy book, but it does not incorporate any real internal tension or overt contradiction.
- All of Isaiah is concerned with Canaanite idolatry. While scholars would expect such a focus from First Isaiah, they would not anticipate it in Second or Third Isaiah (e.g. 57:13); it was not a significant issue to postexilic prophets such as Zechariah, Haggai and Malachi.
- From early on Isaiah promised that the Gentiles would submit to the God of Israel (e.g., 2:2-4), an expectation developed throughout the book (e.g., 42:4; 49:6) and a unifying theological motif for the whole of Isaiah.
Regarding the historical perspective and predictions of Isaiah, the following points are pertinent:
- Isaiah did project himself into the future to describe events as though they had already occurred (e.g. 5:13-17; 9:1-7; 23:1,14). In fact, Isaiah 6, a foundational chapter, presents the exile as inevitable. Isaiah assumed that exile was certain and wrote chapters 40-55 with that in mind.
- Isaiah’s mention of Cyrus’s name has a parallel in the prediction of Josiah’s name in 1 Kings 13:2. It is true that predictions of this kind are fairly rare in the Old testament, but they do occur.
- In contrast to Ezekiel, who lived in Babylon, “Second Isaiah” gave no indication at all that he was familiar with life in Babylon. this suggests that the author of Isaiah 40-55 did not in fact experience Babylonian exile – which is just what we would expect if the chapters were written by Isaiah of Jerusalem.
~ Archaeological Study Bible: The Authorship of Isaiah
In addition to what’s been said, other reasons may be mentioned as well. Why did the redactor (Trito-Isaiah) not change proto-Isaiah from Henotheism to Monotheism? Could it be because the difference is artificial?
Finally, as a personal point, I always thought the mention of Cyrus by name was a strong argument to think that the writer likely lived after the figure of Cyrus who led Israel into the post-exilic period. I did not think this because I doubted the reality of prophecy, but because prophecy rarely (almost never) works without being figurative, and thus it just doesn’t usually mention things by their ‘future’ name. I often wondered what to make of Isaiah 7:14, but I had always been quick to note that it didn’t say ‘Jesus’ but rather some figurative name – without realizing that the name ‘Emmanuel’ did apply to a real child, and Isaiah could have written that before the exile (and before that Child’s birth). As a note in passing though, I had flirted with the idea of saying that First Isaiah wrote the whole prophecy, and some post-exilic redactor inscribed the name ‘Cyrus’ later on, and therefore Cyrus’s name was not good evidence of multiple authorship in the strict sense. However, the alternative example of Josiah in 1 Kings 13:2 is a little eye-opening for me. Prophets did in fact, sometimes, prophesy things by name.
However, it must be realized that this whole thesis of the multiple authorship of Isaiah did not arise in a vacuum; this theory is inexorably linked with the hypothesis of Josiah’s reform and the standard Documentary Hypothesis, which deserves to be brought into serious question.