For example, he sets up a stark debate between Kantian rationalism and Humean emotivism in explaining the basis of human morality; and he argues that empirical research supports emotivism by showing that moral judgment is purely emotional and not rational at all (293-95). This is deceptive in two respects.
First, he does not tell his readers that Hume argued for a combination of reason and emotion in explaining moral judgment. When Hume declared that "reason is, and ought only to be the slave of the passions" (1888, 415), he was not promoting emotivist irrationalism. As the context of this remark makes clear, he believed that reason can direct action but not motivate it: "The impulse arises not from reason, but is only directed by it" (1888, 414). When our passions are accompanied by false judgments, reason can properly correct them: "The moment we perceive the falsehood of any supposition, or the insufficiency of any means or passions yield to our reason" (1888,416). "Reason and judgment may, indeed, be the mediate cause of an action, by prompting, or by directing a passion" (1888, 462). Consequently, "reason and sentiment concur in almost all moral determinations and conclusions" (1902, 172). For example, reason might instruct us as to how justice could be useful to society, but this alone would not produce any moral approbation for justice unless we felt a sentiment of concern for the happiness of society (1902, 285-87).
The second deception is in Prinz's reporting of the experimental research on moral judgment. He correctly reports that that research shows the power of emotion in motivating moral judgment. But he is silent about how that research shows the complex interaction of reason and emotion in ways that confirm Hume's position. For example, Prinz reports the research by Joshua Greene and others who have used functional MRI to scan the brains of people as they make decisions about the Trolley Dilemma. In the Switch Case, most people are willing to pull the switch to save five lives while taking one life. But in the Footbridge Case, most people are unwilling to push the fat man onto the tracks to save five lives. In judging the Switch Case, the more calculating parts of the brain are activated (including the dorsolateral prefrontal cortex), while in judging the Footbridge Case, the more emotional areas of the brain are active (including the ventromedial prefrontal cortex). Here's Prinz's interpretation of this:
"In all these moral dilemmas, there are too options: you can save five people (that's good!), or you can do something that results in one person dying (that's bad!). When you think about doing something good, you may have a positive emotional response; it feels good to help people. When you think about doing something bad, your response is negative. These two emotional forces battle it out in the brain and the stronger one wins." (297)Prinz is silent, however, about the point made by Greene and his colleagues that there is no absolute separation between reason and emotion in the brain. For example, the dorsolateral prefrontal cortex and the ventromedial prefrontal cortex are interconnected, and this confirms Hume insight about the interconnectedness of reason and emotion in moral judgment.
Prinz is also silent about the point made by John Mikhail that the emotional responses to the Trolley Dilemma show an intuitive grasp of the rational principle of double effect. Mikhail generalizes this principle to cover homicide and battery: "the principle holds that an otherwise prohibited action, such as battery or homicide, which has both good and bad effects may be permissible if the prohibited act itself is not directly intended, the good but not the bad effects are directly intended, the good effects outweigh the bad effects, and no morally preferable alternative is available."
Most people think pushing the fat man is wrong because their emotional response against this embodies a rational principle by which a directly intended killing of an innocent person is wrong, while an indirect and unintended killing of an innocent person might be justifiable if it achieves a good effect that outweighs the bad effect.
Emotions are judgments about the world, and thus our emotions are shaped by rational judgments. So, for instance, in the Switch Case, if we discovered that there was some other way to divert the trolley without killing the one innocent person, we would condemn throwing the switch.
Prinz is silent about all of this, because it contradicts his argument for emotivism.
Prinz is also silent about much of what Joseph Henrich and his colleagues have reported in their "Roots of Human Sociality Project," in which they have studied how people in diverse cultures around the world play the Ultimatum Game, the Dictator Game, and the Costly Punishment Game. Prinz reports that people play these games very differently in different cultures, and this shows that there is no universal human nature expressed here, because it shows the cultural relativism of moral judgment. For example, among the Machiguenga of Peru, the average offer in the Ultimatum Game is 26%, which is much lower than the average offer among Americans (310-12).
Prinz is silent about the claim of Henrich and his colleagues that their research show that "fairness and punishment show both substantial variability and reliable patterns across diverse populations." There is great cultural variability, and yet there is a clear pattern in this variation that shows how human culture is constrained by human nature. Offers in the Ultimatum Game were always the most acceptable offer. There were very few offers above 50 percent. No society showed an average offer above 60 percent. So there are no societies where most people give more than half, or where most people give zero. The Hadza foragers were the most selfish people, but even they are not completely selfish. In the Dictator Game, 71 percent of the Hadza offered more than zero. On the other end of the scale, neither do we see completely other-regarding behavior. In the play of the Dictator Game, only three individuals out of 427 offered 100 percent. So Hume was right: human beings are by nature on average neither completely selfish nor completely selfless. Variation in human culture is constrained by the universal pattern of human nature.
Prinz is silent about this. He is also silent about the report of Henrich and his colleagues that belief in a world religion (Islam or Christianity) and market integration promoted higher levels of fairness.
Some of my posts on the Trolley Dilemma and the Ultimatum Game research can be found here, here, here, here, and here.