"As far as we currently know, it is only human beings who can imagine what it is like to be in someone else's shoes. It is an ability with profound effects. It might have helped prehistoric hunters to be able to imagine what their prey would do. Complex human societies would be inconceivable without the ability to imagine what other people might do or wish or fear under particular circumstances. This is different from – and more sophisticated than – simply inferring how another might instinctively react. It is an ability so facile that we often don't even notice it in the course of our busy days.'
"And we go even further. We not only imagine what others are feeling, but also feel something ourselves in response. You see a homeless man shivering on a park bench and you 'feel sorry' for him; that is, you actually feel some measure of discomfort and sorrow. You see the stricken look on a politician's wife as her husband admits to the world that he's been having an affair and you feel embarrassed for her – you may even physically cringe. By the same token, you walk by a small park, see a child swinging as high as she can and loving it, and you feel happy. You may even feel joy. You see newlyweds – even complete strangers – emerging from a church, and feel happy. You see someone arriving at an airport, suddenly surrounded by family and smothered in hugs and kisses, and feel happy for the whole joyous group. Many a camera company has based an advertising campaign on this ability of ours to feel an emotion in response to someone else's experience.'
"This combination of imagining what someone else is feeling and then feeling a related emotion oneself is how I and many (but not all) social scientists define empathy. When the feeling is negative, such as sorrow or embarrassment, in response to another person's experience of something unpleasant, undesirable, or harmful, many social scientists call it empathetic sorrow; a more ordinary word for it is sympathy. When the feeling is positive, such as happiness or pride in achievement, in response to another person's experience of something pleasant, desirable, or beneficial, social scientists call it empathetic joy, but it is telling that there is no ordinary word for that in English."
(pp. 125-6, 'US + Them: Tapping the positive power of difference' by Todd L. Pittinsky – Harvard)