We think of them as killers, outside society. But, says the scientist who has spent his life studying psychopaths, you could have one for a colleague, a friend - or a spouse.
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There are a few things we take for granted in social interactions with people. We presume that we see the world in roughly the same way, that we all know certain basic facts, that words mean the same things to you as they do to me. And we assume that we have pretty similar ideas of right and wrong.
But for a small - but not that small - subset of the population, things are very different. These people lack remorse and empathy and feel emotion only shallowly. In extreme cases, they might not care whether you live or die. These people are called psychopaths. Some of them are violent criminals, murderers. But by no means all.
Professor Robert Hare is a criminal psychologist, and the creator of the PCL-R, a psychological assessment used to determine whether someone is a psychopath. For decades, he has studied people with psychopathy, and worked with them, in prisons and elsewhere. "It stuns me, as much as it did when I started 40 years ago, that it is possible to have people who are so emotionally disconnected that they can function as if other people are objects to be manipulated and destroyed without any concern," he says.