I’d posit the following definitions:

• Empathy: Feeling a similar emotion in response to someone else’s emotional state. Your friend is mad at her boss because he treated her unfairly. That makes you mad at her boss. Your anger is probably different in texture and intensity from hers, but it’s the same in kind, an imperfect reproduction of her mental state.
• Sympathy: Feeling a supportive emotion in response to someone else’s emotional state that is not the same as that person’s original emotion. She is mad at her boss, so you become sorry for her, or committed to fairness, or sad about the state of the world, or nostalgic for better times–but not angry at her boss. Then you are sympathetic. (NB You can be both sympathetic and empathetic if you feel several emotions.)
• Compassion: A species of the genus sympathy. Another person’s negative emotion causes you to have a specific supportive feeling that is not the same as her emotion: you sincerely wish that her distress would end without blaming her for it.
• Justice: A situation or decision characterized by fairness, goodness, rightness, etc. (These are contestable ideas and may be in tension with each other.) The English word “just”–like dikaios in classical Greek–can be applied either to a situation or to a person who cares and aims for justice.

There is an old and rich debate about which character traits and subjective states are best suited to pursuing justice. One answer is that you should be a just person, one who tries to decide what is fair or best for all (all things considered), who desires that outcome, and who works to pursue it. A different response is that we are not well suited to defining and pursuing justice itself. It’s better to cultivate other emotions, such as empathy, sympathy, compassion–or loyalty, aversion to harm, or commitment to specific rules–in order to deliver more just outcomes, all things considered.

I haven’t yet read Paul Bloom’s new book, Against Empathy, but based on this interview and other secondary material, I take it to be an empirically-based contribution to this debate. Bloom marshals evidence that empathy is a highly unreliable guide to justice, probably more likely to mislead than to inform. We should cultivate justice itself, not settle for a substitute, and certainly not the poor substitute of empathy.

For instance, Donald Trump can make people feel empathy for a small number of individuals whose families were allegedly victimized by undocumented aliens, and then use that emotion to build support for deporting millions of people who have harmed no one. A famous example is Edmund Burke’s outrage at the mistreatment of Marie Antoinette, which obscured any concern for the countless people tortured, executed, or “disappeared” by the ancien regime that she represented. (By the way, I happen to respect Burke a lot–and I don’t think it was fair or smart to execute the Queen–but this passage is still a good example of misplaced empathy.)

Empathy can also substitute for justice, as I argued on a visit to Israel in 2013. You congratulate yourself for feeling some version of a suffering person’s emotion and excuse yourself from fixing the problem.

Compassion may be better than empathy. Instead of feeling the same emotion as the other person, you feel a combination of beneficence and equanimity that may be a more reliable guide to acting well. But it’s possible that compassion only clears the deck for reasoning about what you should actually do.

For its part, justice can be emotional. You can feel a powerful urge to make the world more just. That is helpful insofar as the feeling motivates you and insofar as people obtain genuine insights from our emotions; but it is dangerous because the emotion of desiring justice can be misplaced. You can feel great about improving the world when you are actually harming it.

Justice is also necessarily discursive. You must put into words–at least inside your own head–what is good or fair, and why, and make yourself accountable for that position. Therefore, much hinges on whether we human beings can reason explicitly about justice in ways that improve upon our strictly affective reactions to particular situations.

See also: empathy: good or bad?; the limits of putting yourself in their shoes and looking with their eyes; an alternative to Moral Foundations Theory; structured moral pluralism (a proposal); and how to save the Enlightenment Ideal.