L. La Mar Adams, “A Scientific Analysis of Isaiah Authorship,” in Isaiah and the Prophets: Inspired Voices from the Old Testament, ed. Monte S. Nyman and Charles D. Tate Jr. (Provo, UT: Religious Studies Center, Brigham Young University, 1984), 151–64.
The disputed authorship of Isaiah is one of the most popular textual biblical issues and appears to be the father of all Old Testament authorship problems of the same nature.
The majority of biblical scholars divide the book of Isaiah into multiple authorship. The problem of identifying authorship for the book and parts of the book is known as the “Isaiah problem.” Previously, numerous but unsuccessful approaches have been made toward the solution of this problem.
The so-called Isaiah problem dates back to A.D. 1100, when a Jewish commentator named Moses ben Samuel, Ibn-Gekatilla, denied that Isaiah was the author of certain chapters of the book of Isaiah.  Later, in A.D. 1167, Ibn Ezra also questioned the authorship of certain sections of the book of Isaiah.  J. C. Doederlein of the Wellhousen school is credited with having given the theory of multiple authorship its major initial support.  This theory grew until some scholars claimed that the book of Isaiah was a compilation of works from many authors and many periods of time. 
The ancient and formerly unquestioned tradition of the Christian church, inherited earlier from the Jewish tradition, was that the entire book of Isaiah was written by a single author, the prophet Isaiah.  Josephus (ca. A.D. 90) stated that King Cyrus read about himself in the prophecies of Isaiah.  However, the problem of authorship of the book of Isaiah originated among the Jewish sages and received considerable attention among the higher critics of the Old Testament over a period of several centuries. Those most responsible for the early popularity of the theory in the modern era were the biblical critics from Germany, especially Wellhousen. Scholars who divided the book of Isaiah into multiple authorship were referred to as “divisionists”; those who defended single authorship were referred to as “conservatives.” For every conservative scholar today there are eight to ten divisionist scholars.  The vast majority of divisionist scholars divide the book of Isaiah into three authorships which they refer to as Isaiah, Deutero-Isaiah, and Trito-Isaiah. Approximately one-third of the divisionists divide the book into two authorships. Several divisionists maintain that the book is a compilation of many different authors from many different periods of time, and this camp is growing rapidly.  According to some, little remains of the book of Isaiah which can be attributed to the prophet of the eighth century B.C. In his Dictionary of the Bible, John McKenzie claimed:
Most of the book of Isaiah does not come from the Prophet Isaiah, and even those discourses which are his come in the reports of those who wrote them down from auditions or from memory. The book is a compendium of many types of prophecy from diverse periods. 
Edward Young stated that the process of dissection, begun by Bernhard Duhm, probably reached the maximum point of disintegration in the views of Robert Kennett.  Charles C. Torrey complained that the paring process, begun with a penknife, was continued with a hatchet until the book had been “chopped into hopeless chunks.”  An analysis of the divisions postulated by divisionist scholars indicated that there was no agreement between any two of them as to where the division occurred in the book of Isaiah.
The division of the book of Isaiah was followed by authorship division of other Old Testament books by the higher critics, until finally there is no Old Testament book that is not divided into multiple authorship.
In a number of cases, the same evidences, interpreted differently, were given by both divisionists and conservatives in support of their opposing conclusion. Otto Eissfeldt, himself a divisionist, indicated the contradictions in the following quotation:
That there are many common features both in ideas and linguistic usage between XL–LV and LVI–LXVI, is however also admitted by those who do not believe in the identity of the compilers of the two sections. The differences of opinion on this question itself seggests [sic] that the arguments adduced to decide it are ambiguous and can hence be applied in opposite ways. 
Fundamental arguments against Isaiah’s authorship of the entire book may be classified into three basic types: historical, theoretical, and literary. We will first consider the historical arguments.
It was claimed by divisionists that a prophet is sent to prophesy to the people of his own time and that his predictions do not extend beyond the horizon of his own day. Norman Gottwald claimed:
When [the prophetic writings are] studied in their context, apart from dogmatic preconviction, [it is clear that] no prophet leaped across the centuries and foresaw the specific person Jesus of Nazareth. It is a plain violation of historical context to think that they did so, and in practice those that interpret the prophets as predictors of Jesus obscure the setting in which the prophets functioned. 
Historical arguments are often cited by those who advocate multiple authorship. References to historical events such as the conquest of Israel by Assyria,  the Babylonian exile,  and postexilic conditions  were interpreted by divisionists to have been written after the occurrence of such events.
The classical problem cited by Old Testament critics is the prophecy concerning King Cyrus of Persia, who is mentioned by name in Isaiah chapters 44 and 45. It has been argued that Isaiah, living in the eighth century B.C., could not have written the prophecy, since to do so would have required a projection of more than two centuries into the future. The conservatives have argued that the Prophet Isaiah actually predicted events related to Cyrus and Babylonia. R. K. Harrison observed that the conservative scholars cited other Old Testament prophecies which span future centuries to foretell specific names and events (see 1 Kings 13:1f.; Micah 5:2; Ezekiel 26:2ff.; Zechariah 9:lff). 
According to some divisionists, theological concepts such as the majesty of Jehovah in the latter section of the book were fundamentally different than in the first part of the book. Conservatives argue that changes in theological concepts do not imply changes in authorship.
Historical and theoretical arguments have carried relatively little weight with the scholars of the Old Testament, and so the vast majority of the discussion has centered around literary arguments.
The most commonly discussed literary aspect of the book of Isaiah is authorship style. Divisionists claim that they see different authorship styles in the different sections of the book. But conservatives have provided extensive rebuttals to the divisionists’ arguments. James Smart, a divisionist, summed up the situation on both sides of the issue in the following assertion:
An honest recognition of the meagerness of the evidence demands of us a suspension of judgment. Yet one commentator after another has proceeded to base his interpretations upon assumptions that have rested on the flimsiest of foundations. 
What is a scientific approach to the authorship of a book? Simply stated, it is to search out all available evidence, pro and con, to see where the weight of evidence rests. Often, some of the evidence must be put to an appropriate test to see if it is valid and to determine its weight in relation to other evidence. In fact, some types of evidence outweigh all the others put together.
Where would we start looking for a scientific approach to an analysis of the authorship style in the book of Isaiah? Would we begin by asking what evidence exists? In response to these questions, a survey was made several years ago of all available literature on the so-called Isaiah problem.  Claims made by all the various authors were tabulated into various categories of pro and con in relation to the claim for single authorship of the book of Isaiah. Some divisionists assert that no literary evidence exists for authorship unity of the book. One German critic, Georg Fohrer,  claimed that all literary evidence points to multiple authorship. The divisionists emphasize the literary differences between the various sections of Isaiah, and conservatives the similarities.
The above-mentioned research, which we will now examine, involved a computer and thirty-five researchers and associates across several disciplines at Brigham Young University over a period of three years. It was designed to test the validity of claims made by the biblical scholars.
Since divisionists have claimed that authorship styles of speaking and writing vary significantly in the different sections of the book of Isaiah, the literary elements given as evidence were examined with the help of the computer to test the validity of these claims. Claims made by the conservative scholars were also tested.
Analysis of authorship style of this nature involves comparing the rates of usage of literary elements in one section of the book with rates of usage in another to determine if the rates of usage are the same in both sections. The method used compares the rates by means of computerized statistical procedures. However, the type of statistical analysis is determined by the type of literary elements being analyzed and the manner in which they are to be analyzed. For example, one cannot select just any literary element to compare authorship styles between two texts, since many literary elements are used at different rates and in different ways by any given author from one context to another. If a young man writes a letter to his sweetheart, it is expected to contain certain types of words and expressions not expected to be found in a letter the same young man may write in protesting some government action. Therefore, some claims made by biblical scholars, conservative or divisionist, may be valid but are not evidence of either single or multiple authorship. This was found to be the case when many claims of the biblical scholars were put to the test. For example, on one hand, the use of war terminology claimed by Yehuda Radday to be evidence of multiple authorship was found to be based on an invalid assumption.  On the other hand, many of the conjunction words claimed by the conservative scholar Letitia D. Jefferys to be evidence of single authorship were found to be unsupportive of her claims.  These two examples also serve as instances of the use of literary variables which do not serve as evidence in an authorship study of this type.
In a valid study, the literary variables examined must be the type that identify authorship styles unique to the author. The best kind of literary element for this type of analysis consists of habit-prone parts of speech. Identification of habit-prone types of speech, particularly those that are used subconsciously, is extremely difficult, especially in the English language. However, in classical Hebrew there is a prefix characteristic which makes it possible to identify many habit-prone parts of speech by use of computerized statistical analysis. This type of prefix is referred to as a “function prefix.” The use of certain words and prefixes is influenced more by the context of the writing than by the authorship style. Pronominal, verbal, and participial prefixes are judged to be too contextually oriented for authorship identification. Therefore, function prefixes include all prefixes except those which are pronominal, verbal, and participial.
The purposes of this study were twofold: (1) to statistically analyze the validity of the claims and the supportive materials for and against the unity of Isaiah authorship as made by biblical scholars in the available literature, and (2) to provide a valid computerized statistical approach in determining authorship of the book of Isaiah.
Computer programs were written to obtain data for analyzing the validity of claims made by scholars concerning the Isaiah problem. The Hebrew text was used for analysis, including the complete Hebrew text of the book of Isaiah, and random samples from eleven additional Old Testament books were used. (The eleven additional books, selected by stratified random sampling, were Amos, Jeremiah, Ezekiel, Hosea, Micah, Habakkuk, Zechariah, Daniel, Ezra, Malachi, and Nehemiah. These books served as Hebrew control texts for comparison with the book of Isaiah.) The book of Isaiah was divided into the various sections suggested by divisionists. The major sets of divisions analyzed for authorship style consisted of the following:
- The commonly used twofold: Chapters 1–39 and 40–66, the so-called Deutero-Isaiah.
- The more popular threefold division: Chapters 1–39, 40–55, and 56–66, the so-called Trito-Isaiah.
- Radday’s division: Chapters 1–12, 13–23, 24–35, 36–39 (omitted by Radday), 40–48, 49–57, and 58–66.
- Driver’s division: Chapters 1–12, 13–23, 24–27, 28–33, 34–35, 36–39, 40–48, 49–55, 56–62, and 63–66. 
This study is the most extensive to date. Specialists in the areas of Semitics, languages, statistics, and computer science were involved. Over seventy different types of stylistic elements were examined, and several hundred linguistic variables were analyzed. The major analysis consisted of comparing the rate of usage of literary variables with authorship styles across the different sections of Isaiah. Similar comparisons were made within and between the eleven Old Testament control texts and the book of Isaiah.
Among all the statistical elements examined in this study, the function prefix provided the most valid approach. The book of Isaiah has a surprisingly large number of function prefixes indicating single authorship. Out of 36 different prefixes and prefix combinations examined in the Hebrew text,  occurred in the book of Isaiah. The accompanying table shows the usage frequency of 18 of these 24 function prefixes. Although each of the 18 prefixes was used in both sections in the book of Isaiah (chapters 1 to 39 and 40 to 66), some of the prefixes were not found in a number of the control texts.
It is evident from the last two columns in the table (Isaiah A and Isaiah B) that the rates of usage for a number of prefixes show a similarity between the two Isaiah texts that is peculiar to the book of Isaiah and contrasts markedly with the control texts. For example, both Isaiah sections have a rate of 2 (equivalent to .02 per 50 prefixes) for the prefix bet-mem (shown as BM in the table) compared to .00 for each of the control texts. (The .00 indicates that this function prefix was not used in the control text.)
Another example of uniqueness in the book of Isaiah may be observed in the usage rate of the prefix vav-lamed (VL in the table) in the English text. Isaiah 19:24 concludes with a description of a condition in the millennial era: “In that day shall Israel be the third part with Egypt and with Assyria.” In this phrase, the Hebrew prefix vav-lamed is rendered “and with.” This prefix combination may also be translated as “and to.” In Isaiah 60:9 we read the phrase “to bring thy sons . . . unto the name of the Lord thy God, and to the Holy One of Israel.” This has reference to the gathering of exiled Israel in the latter days.
The usage rate for vav-lamed is unique to the book of Isaiah, occurring approximately .68 times for every 50 function prefixes in Isaiah A and .67 times per 50 prefixes in Isaiah B, compared to a zero rate (that is, almost never) for such books as Amos, Micah, and Ezekiel. Usage of this prefix occurs at a high rate of 2 per 50 prefixes in the book of Nehemiah, as exemplified in Nehemiah 2:16: “Neither had I as yet told it to the Jews, nor to the priests, nor to the nobles, nor to the rulers, nor to the rest that did the work.’’
One example of a function prefix which serves as an idiomatic part of speech is the one which translates into “and in this.” The rate of usage of this phrase was found to be constant across the different sections of the book of Isaiah, in contrast to the rates of usage in other Old Testament texts. This phrase and the other function prefixes in the table had usage rates so peculiar to the book of Isaiah that single authorship was strongly evident.
In this phase of the analysis we drew heavily on the statistical expertise of Dr. Alvin Rencher, presently chairman of the BYU Statistics Department. We found that the authorship style was more consistent in the book of Isaiah than in any of the other Old Testament books we examined. Some otherwise conservative scholars who have ascribed the book of Isaiah to the prophet Isaiah claim that the historical chapters 36 to 39 were written by another author. However, the results of this study indicate that chapters 36 to 39 are not to be denied the prophet Isaiah. Even the ten verses by King Hezekiah in chapter 28 may have been written in the original records by Isaiah. There is some evidence that a later transcriber abridged the text. However, such alterations were evidently not extensive enough to camouflage the literary style of the original author.
The statistical results in this study do not support the divisionists’ claim that little or no evidence exists for unity of the book of Isaiah. To the contrary, the results strongly support single authorship of the book. The divisions of the book most often claimed to have been written by different authors were found to be more similar to each other in authorship style than to any of the control group of eleven other Old Testament books. The book of Isaiah also exhibited greater internal consistency than any of the other books when authorship style was analyzed.
These results do not exclude the possibility that minor changes in the text have been made by scribes and editors since the time of its origin. However, the evidence indicates that in spite of such possible changes, an overall style has been retained as measured by the literary variables examined. The results of this research bear witness that the book of Isaiah has a literary unity characteristic of a single author. These results, therefore, confirm the claims made in the Book of Mormon and the New Testament by later prophets and by the Savior that Isaiah was the author of the book bearing his name.
Previous attempts at computerized statistical analysis of the book of Isaiah were made by two different researchers, Yehuda Radday24 and Asa Kasher.  Both of these researchers independently concluded that the book of Isaiah was written by multiple authors. Radday’s work was based on an inappropriate assumption: he assumed that a difference in the usage of one type of word (such as war terminology) from one section or prophecy to another was an indication of a difference in authorship. To demonstrate the invalidity of his method, we applied Radday’s procedures to a text known to have been written by Thomas Carlisle. The result was a false conclusion that part of Carlisle’s text was written by another author. 
Kasher’s approach was likewise analyzed and found to be based on inappropriate assumptions. I have corresponded extensively with these two Israeli researchers, and they are aware of the problems in their research.
Why do most biblical scholars insist on multiple authorship for the book of Isaiah? Evidently the reason lies in the fact that the scholars do not believe that a prophet can prophesy beyond his own time period. George Robinson summarized the arguments postulated by divisionists against futuristic prophecy:
The fundamental axiom of criticism is the dictum that a prophet always spoke out of a definite historical situation to the present needs of the people among whom he lives, and that a definite historical situation shall be pointed out for each prophecy. This fundamental postulate . . . underlies all modern criticism of O. T. prophecy. 
Harrison claimed that argument concerning prophecy was embarrassing to critical scholars:
On the basis of their insistence that there was no predictive element in prophecy, they tried to dismiss the problem or more commonly, to avert the critical gaze from it. 
Why is it that the critics do not believe in the type of revelation that allows prophets to give futuristic prophecy? The Savior himself answered this question:
He that believeth not is condemned. . . . And this is the condemnation, that light is come into the world, and men loved darkness rather than light, because their deeds were evil. For every one that doeth evil hateth the light, neither cometh to the light, lest his deeds should be reproved. (John 3:18–20.)
Denial by critics that certain prophecies in the book of Isaiah were written by the prophet himself fulfill, at least in part, an ancient prophecy ascribed to Isaiah in an apocryphal work entitled the “Ascension of Isaiah” (3:30-31):
For there will be great jealousy in the last days; for everyone will say what is pleasing in his own eye. And they will make of none effect the prophecy of the prophets which were before me, and these my visions also, will they make of none effect in order to speak after the impulse of their own hearts. 
We are living in a day when the prophecies of Isaiah are being fulfilled. These evidences that the book of Isaiah was written by the prophet Isaiah help us understand his prophecies. They also serve as an additional witness to the truthfulness of the Book of Mormon and New Testament statements from prophets and the Savior concerning the words of Isaiah. Together they all help to bring us closer to the Lord. If we are to go where Isaiah goes, we will need to know what Isaiah knows. The more we read the words of Isaiah, the more we will become like him, the other prophets, and the Savior.
 Edward J. Young, An Introduction to the Old Testament (Grand Rapids, MI: Eerdsmans, 1949), 199.
 George A. Buttrick et al., eds., The Interpreter’s Bible, vol. 5 (New York: Abingdon Press, 1956), 382.
 R. K. Harrison, Introduction to the Old Testament (Grand Rapids, MI: Eerdmans, 1969), 763.
 John L. McKenzie, Dictionary of the Bible (Milwaukee: Bruce, 1965), 397.
 Sidney B. Sperry, The Voice of Israel’s Prophets (Salt Lake City: Deseret Book, 1961), 84; Larry L. Adams, “A Statistical Analysis of the Book of Isaiah in Relation to the Isaiah Problem” (PhD dissertation, Brigham Young University, 1972), 10–11.
 Flavius Josephus, Josephus: Complete Works, trans. William Whiston (Grand Rapids, MI: Kregel, 1960), The Antiquities of the Jews, XI:l:lf.
 Adams, 19–23.
 Ibid.; also Georg Fohrer, Introduction to the Old Testament (New York: Abingdon Press, 1967), 385.
 McKenzie, 387.
 Edward J. Young, Who Wrote Isaiah? (Grand Rapids, MI: Eerdmans, 1958), 20.
 Charles C. Torrey, The Second Isaiah (New York: Scribners, 1928), 13.
 Otto Eissfeldt, The Old Testament: An Introduction, trans. Peter R. Ackroyd (Oxford: Basil Blackwell, 1966), 342.
 Norman K. Gottwald, A Light to the Nations: An Introduction to the Old Testament (New York: Harper, 1959), 275.
 Aage Bentzen, Introduction to the Old Testament, 2 vols. (Copenhagen: Gads Forlag, 1949), 2:107.
 Christopher R. North, The Second Isaiah (Oxford: Clarendon Press, 1964), 3.
 Claus Westermann, Isaiah 40–66 (Philadelphia: Westminster Press, 1969), 296–99.
 Harrison, 765.
 James D. Smart, History and Theology in Second Isaiah (Philadelphia: Westminster Press, 1965), 30.
 Adams, 10–42.
 Fohrer, 385.
 Adams, 90–92.
 Ibid., 107–18.
 L. La Mar Adams and Alvin C. Rencher, “A Computer Analysis of the Isaiah Authorship Problem,” BYU Studies 15 (Autumn 1974): 97.
 Yehuda T. Radday, “The Unity of Isaiah: Computerized Test in Linguistics” (unpublished report, Israel Institute of Technology, 1970).
 Asa Kasher, “The Book of Isaiah: Characterization of Authors by Morphological Data Processing” (unpublished essay, Department of Mathematics, Bar-Ilan University, Ramat-Gan, Israel, 1970).
 Adams, 93–95.
 George L. Robinson, “Isaiah,” in The International Standard Bible Encyclopedia, ed. James Orr, 5 vols. (Grand Rapids, MI: Eerdmans , 1960), 3:1505.
 Harrison, 776.
 L. La Mar Adams, The Living Message of Isaiah (Salt Lake City: Deseret Book, 1981), 111.