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Appeal to emotion or argumentum ad passiones is a logical fallacy characterized by the manipulation of the recipient's emotions in order to win an argument, especially in the absence of factual evidence. This kind of appeal to emotion is a type of red herring and encompasses several logical fallacies, including appeal to consequences, appeal to fear, appeal to flattery, appeal to pity, appeal to ridicule, appeal to spite, and wishful thinking.
Instead of facts, persuasive language is used to develop the foundation of an appeal to emotion-based argument. Thus, the validity of the premises that establish such an argument does not prove to be verifiable.
Appeals to emotion are intended to draw inward feelings such as fear, pity, and joy from the recipient of the information with the end goal of convincing him/her that the statements being presented in the fallacious argument are true.
The power of emotions to influence judgment, including political attitudes, has been recognized since classical antiquity. Aristotle, in his treatise Rhetoric, described emotional arousal as critical to persuasion, "The orator persuades by means of his hearers, when they are roused to emotion by his speech; for the judgments we deliver are not the same when we are influenced by joy or sorrow, love or hate." Aristotle warned that emotions may give rise to beliefs where none existed, or change existing beliefs, and may enhance or decrease the strength with which a belief is held. Seneca similarly warned that "Reason herself, to whom the reins of power have been entrusted, remains mistress only so long as she is kept apart from the passions."
Centuries later, French scientist and philosopher, Blaise Pascal wrote that "People [...] arrive at their beliefs not on the basis of proof, but on the basis of what they find attractive."Baruch Spinoza characterized emotions as having the power to "make the mind inclined to think one thing rather than another." Disagreeing with Seneca the Younger that emotion destroys reason, the 18th century Scottish philosopher George Campbell argued, instead, that emotions were allies of reason, and that they aid in the assimilation of knowledge. However, Campbell warned of the malleability of emotion and the consequent risk in terms of suggestibility:
Drawing on the social psychology of his day, propaganda theorist Edward Bernays confidently asserted that "in certain cases we can effect some change in public opinion with a fair degree of accuracy by operating a certain mechanism, just as a motorist can regulate the speed of his car by manipulating the flow of gasoline."  Bernays advised that to change the attitudes of the masses, a propagandist should target its "impulses, habits and emotions"  and make "emotional currents" work to achieve the goal.
Indeed, some contemporary writers have attributed the popularity of the most destructive political forces in modern history--from Nazism to Jihadism--to the ability of their leaders to enchant (rather than convince) publics and to oppose "the heavenly ecstasies of religious fervor" to the "naked self interest" and the icy, individualistic rationalism of modern liberalism.
Similarly, Drew Westen, professor of psychology psychiatry and behavioral sciences at Emory University, drawing on current psychiatric and psychological research to demonstrate the power of emotions in affecting political cognition and preferences, wrote that, "when reason and emotion collide, emotion invariably wins."  Westen, an advisor to Democratic political campaigns, believes that evolution has equipped people to process information via emotions and that people respond to emotional cues more than to rational arguments. Accordingly, Westen believes that emotion lies at the center of effective persuasion and that appeals to emotion will always beat appeals to reason:
A social psychology theory posits that attitudes have three components -- affect, cognition and behavior. The cognitive dimension refers "to beliefs that one holds about the attitude object, and behavior has been used to describe overt actions and responses to the attitude object." Affect, meanwhile, describes "the positive and negative feelings that one holds toward an attitude object", that is, the emotional dimension of an attitude. Modern theorists have modified the tripartite theory to argue that an attitude "does not consist of these elements, but is instead a general evaluative summary of the information derived from these bases."
Political scientist George Marcus (writing with Russell Neuman and Michael Mackuen) identifies two mental systems through which reason and emotion interact in managing and processing political stimuli:
The second system, the surveillance system, "acts to scan the environment for novelty and sudden intrusion of threat." In other words, the second system monitors the environment for any signs of threat. If a threat is found, that system takes people out of habitual, casual processing and puts them in a state of alertness and receptivity to new information:
Marcus further argues that "emotional engagement will motivate people toward making more deeply reasoned decisions about politics than those who remain dispassionate." Other thinkers have argued that "when an emotion is aroused and experienced, it can involve a number of psychological processes that can then be used as a platform for promoting and securing influence and compliance."
Regardless, it would stand to reason, then, that affecting a subject's emotional state, in conjunction with a political message, could affect that subject's attitudes.
In modern philosophy, there are two core appeals to emotion. One is the appeal to force (known as ad baculum) the other is the appeal to sympathy, known as ad misericordiam. These are only considered fallacies when used in doxastic systems.
Accepted wisdom[who?] is that, "[w]hen it comes to issues of emotional importance, convincing someone to change his or her existing beliefs appears to be a virtually hopeless undertaking."  And yet, manipulating emotions may hold the key to shaping attitudes:
Though it is still a very undeveloped area of research, a number of scholars are demonstrating that manipulating emotions surrounding a persuasive message does affect that message's effectiveness. It has been shown, for example, that people tend to adjust their beliefs to fit their emotions, since feelings are treated by people as evidence, and when feelings match beliefs, that is seen as validation of the underlying beliefs. Other research shows that "emotional stimuli can influence judgment without a judge's awareness of having seen or felt anything (e.g., Bargh, 1997; Murphy & Zajonc, 1993)."
Indeed, "recent studies have confirmed that affect does play a general role in attitude change, whether due to persuasive communication, or to cognitive dissonance processes (Petty et al., 2001)."
Psychologists Petty & Cacioppo found that there are two ways of processing persuasive messages: (1) to focus on the content and quality of the message (central processing), or (2) to focus instead on external cues (such as the source of the message) and to disregard its content (peripheral processing). "When participants use the central/systematic route of responding to message content, they tend to be persuaded more by strong arguments, and less by weak arguments. However, the strength of the argument matters less when the peripheral route is chosen. In that case, other "peripheral" factors, such as the credibility of the source of the message or the intention of the communicator become important in the persuasive process." Petty and Cacioppo suggest that negative affect should lead to more central processing and positive affect to more peripheral processing. That is, "In happy moods, people tend to be persuaded equally by strong and weak arguments, whereas in sad moods, people are persuaded only by strong arguments and reject weak arguments." Said otherwise, positive moods increase the reliance on positive beliefs, whereas negative moods encourage the updating of beliefs in the light of new, significant data.
Drawing on the work of Marcus, political scientist Tom Brader says that, "by appealing to specific emotions, [communicators] can change the way citizens respond to political messages."
The only widely studied emotion, with respect to persuasion, is fear. Fear has been found to force individuals "to break from routine and pay close attention to the external world," including persuasive messages. Moreover, fear has been found to encourage political engagement:
More generally, "fear is associated with both attitude and behavior change."  However, "four variables that may interact to influence processing depth of a fear-inducing message: (a) type of fear (chronic vs. acute), (b) expectation of a message containing reassuring information, (c) type of behavior advocated (e.g., disease detection vs. health promotion), and (d) issue familiarity."
Guilt is the emotion that arises when an individual breaks an internalized moral, ethical or religious rule. Guilt's effect on persuasion has been only cursorily studied. Not unlike fear appeals, the literature suggests that guilt can enhance attainment of persuasive goals if evoked at moderate levels. However, messages designed to evoke high levels of guilt may instead arouse high levels of anger that may impede persuasive success.
Anger's effect on persuasion has also seldom been studied. A couple of studies, however, "suggest that a positive relationship exists between anger and attitude change." Specifically, researchers found that "anger evoked in response to issues of juvenile crime and domestic terrorism correlated with acceptance of legislative initiatives proposed to address those issues." Not unlike fear, anger was associated with close (central) information processing including of persuasive messages. At the same time, "unintentionally induced anger in response to supposed guilt and fear appeals has been shown to correlate negatively with attitudes."
Sadness arousal has been associated with attitude change in the context of AIDS, illicit drugs, and juvenile crime.
Disgust arousal, in the context of messages opposing animal experimentation, is correlated negatively with attitude change. This is consistent with the view that disgust leads to a rejection of its source.
A number of recent studies support the role of compassion in skewing moral judgment. The researchers' findings show there is a key relationship between moral judgment and empathic concern in particular, specifically feelings of warmth and compassion in response to someone in distress.
Images of suffering children are the ideal triggers of this instinctive compassion.
Once triggered, compassion leads individuals to favor the few they see suffering over the many who they know to be suffering but in the abstract: "People who feel similar to another person in need have been shown to experience more empathic compassion for that person than do those not manipulated to feel similar to another."
Dan Ariely notes that appeals that, through visual cues or otherwise, make us focus on specific, individual victims affect our attitudes and lead us to take action whereas, "when many people are involved, we don't. A cold calculation does not increase our concern for large problems; instead, it suppresses our compassion."
"Little studied in the social influence context, the one clearly identifiable study of pride and persuasion considered the role of culture in response to advertising, finding that members of a collectivist culture (China) responded more favorably to a pride-based appeal, whereas members of an individualist culture (the United States) responded more favorably to an empathy-based appeal." 
Some researchers have argued that anxiety which is followed by relief leads to greater compliance to a request than fear, because the relief causes a temporary state of disorientation, leaving individuals vulnerable to suggestion. The suggestion is that relief-based persuasion is a function of less careful information processing.
Experiments have shown that hope appeals are successful mainly with subjects who self-report as being predisposed to experiencing fear