Part 4 of a Series on Persuasion
Kriesberg refers to appeals to common values and norms. Such appeals are often referred to as appeals to conscience. Appeals may also be made to the other's emotions or to data and logic.
Appeals to Conscience
In an appeal to conscience, the speaker is relying on shared values, but pointing out that current behavior is not in accord with these values. While none of us act in accord with our values at all times and in all places, "we nonetheless feel uncomfortable when made aware of inconsistencies. When these inconsistencies become obvious, we feel a strain to change."  For the speaker to have the higher ground, however, it is crucial that she or he is seen as acting in accord with these values.
Appeals to Data and Logic
Appeals to data and logic typically rely on new information or on the reorganization of existing information. The landmark U.S. Supreme Court decision Brown v. Board of Education, which de-segregated American schools, provides a good case in point. Court decisions are usually justified in terms of case precedent. To overturn Plessy v. Ferguson and do away with the principle of "separate but equal" in public education, however, the Court relied largely on the social sciences, stating that:
Whatever may have been the extent of psychological knowledge at the time of Plessy v. Ferguson, [our] finding is amply supported by modern authority. 
The modern authorities to whom the Court was referring included noted psychologist Kenneth B. Clark and sociologist Gunnar Myrdal, both of whom had researched the impact of racial segregation. Clark had used dolls to determine that black children's self-esteem was damaged by segregation.  Myrdal's monumental American Dilemma documented the persistence of the discrepancy between the American creed and treatment of African Americans in all areas of life.  The Court not only based its decision on such data, but avowedly chose to utilize these data as opposed to other legal arguments.
Thurgood Marshall and the other NAACP (National Association for the Advancement of Colored People) attorneys (the plaintiffs) were not the only ones using persuasive power effectively in the case. The Supreme Court justices did too, in an effort to convince each other. Some of the justices were inclined to vote to maintain the separate but equal policy. In fact, had the vote been taken after initial arguments, it is highly likely that Brown v. Board would have been just one more in a long line of failed attempts to overturn segregation. However, Justice Frankfurter convinced his colleagues to delay the decision and call for rehearing the case. Then, newly appointed Chief Justice Earl Warren used his adroit negotiation skills and succeeded in getting a unanimous decision in favor of the plaintiffs. 
Aristotle identifies an effective emotional appeal, "excit(ing) the required state of emotion in your hearer," as an integral aspect of the final stage in an argument.  At the outset of Rhetoric, however, he points out that "the arousing of prejudice, pity, anger, and similar emotions has nothing to do with the essential facts, but is merely a personal appeal to the man who is judging the case." Later, he states more strongly: "It is not right to pervert the judge by moving him to anger or envy or pity -- one might as well warp a carpenter's rule before using it."  This identifies the dilemma of emotional appeals. A strong argument needs facts at its base, and even the strongest may not "move" the other to change behavior without an appropriate emotional appeal.
Example: Martin Luther King's "Letter from a Birmingham Jail"
Martin Luther King Jr.'s "Letter from a Birmingham Jail," while primarily an appeal to conscience, is masterful in its combination of types of appeals. It weaves them together for greatest impact, and utilizes many of the principles of influence identified above.
King opens the letter "MY DEAR FELLOW CLERGYMEN." He thus establishes kinship with his audience from the outset with the word "fellow"; later on he deepens the connection, calling them "my Christian and Jewish brothers." He provides data to counter perceptions of himself as an "outside agitator," providing information on his "organizational ties" and claiming his insider role as an American citizen. Maintaining his connection with the clergy while moving to an appeal to conscience, he connects his journey to Birmingham to the role of Biblical prophets. Prophecy was a ministry with which his addressees were not only familiar, but which they preached from their own pulpits:
Just as the prophets of the eighth century B.C. left their villages and carried their "thus saith the Lord" far beyond the boundaries of their home towns, and just as the Apostle Paul left his village of Tarsus and carried the gospel of Jesus Christ to the far corners of the Greco-Roman world, so am I compelled to carry the gospel of freedom beyond my own home town.
Much of the letter provides information. King presents his reasons for being in Birmingham and lays out the horrible impacts of prejudice in what was "probably the most thoroughly segregated city in the United States." He also provides a brief explanation of the principles of nonviolent action. King points out that he and the other protestors had followed the rubric of seeking solution prior to protest. He provides information on how the organizers undertook the first three stages -- collection of facts, negotiation, and self-purification -- before embarking on direct action.
King's appeals to emotion, particularly guilt, stand out in the letter. The entirety of the letter is written in calm tones, expressing disappointment rather than anger. King conveys his recurrent hope that the white churches will see the injustice of racism and rally to the cause of the civil-rights movement. He acknowledges those who have done so, but the reader can almost see the tears behind his cataloguing of the many times and ways in which those hopes have been dashed. The penultimate paragraph is a particularly well-stated summary of his guilt-provoking stance:
If I have said anything in this letter that overstates the truth and indicates an unreasonable impatience, I beg you to forgive me. If I have said anything that understates the truth and indicates my having a patience that allows me to settle for anything less than brotherhood, I beg God to forgive me.
While most of the letter is calm and reflective in tone, begging reconsideration rather than fostering defensiveness, its most-often-quoted sentences are a rousing call to the struggle for justice:
"Injustice anywhere is a threat to justice everywhere. We are caught in an inescapable network of mutuality, tied in a single garment of destiny. Whatever affects one directly, affects all indirectly."
I have chosen to draw my references to the "Letter from a Birmingham Jail" from a current peace-studies reader rather than from its original source or from King's collected writings and speeches. Doing so underscores something else about the persuasive power of carefully expressed appeals. Although the letter was written to eight clergymen who had questioned his presence in Birmingham and the tactics his followers were using, it was broadcast well beyond the original addressees in both space and time. Whatever the impact it had on them, it has stirred countless others to action and served as an inspiration to those involved in nonviolent struggles for justice.
Example: Morton Deutsch
To extend our discussion of effective appeals, we examine Morton Deutsch's strategy for persuading the United States and the Soviets to change their hostile orientation during the Cold War. Though now ended, the Cold War was at the time (early 1960s) a conflict that not only seemed to be intractable, but which threatened the survival of everyone on the planet, regardless of whether they were citizens or allies of one of the principals or not. Drawing on his experience as a psychotherapist, he suggested "four critical tasks" in persuading an enemy to change its hostile stance:
First of all, there must be some motivation to change -- the gains (the adversaries) derive from a hostile orientation must not be so great as to outweigh the anxieties and difficulties of the present situation.
Second, they must be made aware that the experiences anxieties and difficulties are causally connected with their competitive, hostile orientation.
Third, the current environment must not provide substantial justification and support for the continued maintenance of the defensive, hostile orientation appropriate in the past: new experiences, convincingly different from their past experiences, must indicate a genuine interest in their well-being.
Fourth, they must perceive that they will gain rather than suffer, have less anxiety rather than more, if they adopt a new orientation.
Deutsch's third task suggests that, in order to persuade an enemy, a party must be willing to reassess its own behavior and make changes. Without real behavioral changes on the part of the persuader, persuasive efforts are likely to fall flat. Words alone, no matter how impassioned or logically cogent, are likely to be insufficient.
 Trenholm, Sarah. Persuasion and Social Influence. Englewood Cliffs, N.J.: Prentice-Hall, Inc., 1989, p. 111, http://www.amazon.com/Persuasion-Social-Influence-Sarah-Trenholm/dp/0136611176.
 "Kenneth B. Clark, activist, psychologist, and author," The African American Registry, http://www.aaregistry.org/historic_events/view/kenneth-b-clark-pioneering-educator-and-psychologist.
 Zhang, Junfu. "Black-White Relations: The American Dilemma," Perspectives, I (4), http://www.oycf.org/Perspectives2/4_022900/black_white.htm.
 Roberts, Paul Craig and Lawrence M. Stratton, "The Brown Decision," from The New Color Line: How Quotas and Privileges Destroy Democracy, 1995, http://www.lewrockwell.com/orig/brown.html.
 Aristotle. Rhetoric. Based on 1954 translation by W. Rhys Roberts. Hypertext editor: Lee Honeycutt. Part 1, http://homepage.cs.uri.edu/courses/fall2007/csc305/Schedule/rhetoric/1index.htm, Part 3 http://homepage.cs.uri.edu/courses/fall2007/csc305/Schedule/rhetoric/3index.htm.
 Aristotle, Part I
 King, Martin Luther Jr. "Letter from a Birmingham Jail, " in A Peace Reader: Essential Readings on War, Justice, Non-violence and World Order. New York: Paulist Press, 1992, p. 115, http://books.google.com/books?id=I5e1oWb7zSUC.
 King, p.128.
 King, p.115.
 Deutsch, Morton, "Producing Change in an Adversary," in International Conflict and Behavioral Science: The Craigville Papers. ed. Roger Fisher. New York: Basic Books, Inc., 1964, p. 151.
By Máire Dugan