Why "reasonable" people so often disagree? Isn't the "evidence" for or against a particular position there for all to see? Dr. Ullmann-Margalit makes a conjecture that helps to understand the phenomenon: the way even the scholars view the evidence is heavily, and often decidedly influenced by their prior assessment of the likelihood (or probability) of the phenomenon the evidence is confirming. "Their very description (or "framing") of the evidence will depend on their degree of belief in the theory being tested".
The overall aim of Dr. Ullmann-Margalit is to examine the field of Qumran Studies, and specifically the Essene connection to the Dead Sea Scrolls. For this, in the first chapter she briefly, but succinctly, sets out to acquaint the reader with the background facts, including the history of discovery of the Dead Sea scrolls, and the subsequent scholarship. The main controversy surrounding the Dead Sea scroll study is whether or not they can be attributed to the Essenes - a Jewish sect residing in a nearby settlement - Qumran. Whereas the Qumran-Essene connection is currently the prevailing view, Dr. Ullmann-Margalit points out numerous inconsistencies in the evidence. Specifically, as pointed out in the review of the book by the pre-eminent philosopher Sir Anthony Kenny "...Ullmann-Margalit claims that researchers, instead of respecting the independence of the sources, have allowed them to contaminate each other. Thus the archaeological data are presented not neutrally but in the light of an interpretation of the Scrolls... Instead of a convergence of evidence, she claims, we meet an interpretive circle". (The Times Literary Supplement, October 24, 2008).
In the monumental second chapter, Dr. Ullmann-Margalit attempts and succeeds in taking a "Hard look at the "hard facts"": by analyzing the actual archaeological findings and their interpretations by different scholars. In a wonderfully clear and precise language, she explains the concepts of prior and posterior probabilities for hypothesis formation (the Bayesian theory) and proceeds to demonstrate in specific concrete cases how these prior assessments critically affect conclusions made by different scientists based on the same evidence. The examples include "negative findings" - contradicting the Essene hypothesis, such as some military objects which contradict a description of Essenes as peace-loving people, and "affirmative findings", such as ritual baths. Dr. Ullmann-Margalit proceeds with her analysis and, drawing from wide range of concepts including philosophy, statistics, and psychology, shows how these same facts are interpreted by scholars depending on their own pre-conceived ideas. One interesting general example of this mechanism is the so-called "confirmation bias": a tendency of people to pay more attention to the evidence that confirms, rather than contradicts their own hypotheses. By analyzing the evidence itself, and the various interpretations, Dr. Ullmann-Margalit says that "....when a find is consistent with the researcher's favorite theory, the confirmation bias will make them consider the find as supporting the theory. When the find is not merely consistent but also unique .... the researchers will tend to consider the support this finding lends to the theory all the more dramatic or striking. A find that is inconsistent with one's favorite theory, on the other hand, needs to be explained away. But when inconsistent finding happens to be unique .... it becomes that much easier for the researchers simply and safely to ignore it. In other words, unique items somehow seem to score extra points when they are positive, and to be more easily discarded when they are negative". Thus, Dr. Ullmann-Margalit points out that the controversy reflects the disagreement of the scholars about the evidence, because of the interdependence of theories and the evidence.
In the third chapter, Dr. Ullmann-Margalit shows that the scholars even disagree on how to name the sect that wrote the scrolls, finally settling on what Dr. Ullmann-Margalit calls "a circular and vacuous label": the scroll sect. Noting this, Dr. Ullmann-Margalit then proceeds on her own to question even the assumption that the scrolls are written by a "sect", and specifically by a sect leading to Christianity, as advocated by some Christian scholars.
For the conclusion, I will quote again Sir Anthony Kenny: " For all those interested in the Dead Sea Scrolls, Out of the Cave provides a lucid intellectual structure for the classification and evaluation of Qumranologists. But the book could also serve as an introductory text in philosophy of science. Introducing, with an admirably light touch, classical theories from Bayes to Popper and currently popular models of inference to the best explanation, the author uses scrolls research as a test-bed for the logic of discovery and argument in the human sciences".