Recent experiments suggest that triggering humans’ disgust instinct can alter their moral reasoning about everything from homosexuality to war.

Question: How does disgust inform our moral reasoning?

Paul Bloom: There's a big debate in the field over how we make our moral judgments. And a lot of scientific debates are fairly abstract and don't connect to public policy, but this matters. Because this asks questions like, what underlies our intuitions about abortion? Or gay marriage? Or the war in Afghanistan? And a lot of psychologists push a very hard line here, arguing that our moral intuitions are driven by gut feelings, by gut emotional reactions. We might tell these elaborate stories, "Oh, I think gay marriage is fine because I get a bunch of arguments," but the arguments really have nothing to do with why I've come to my opinion. I've come to my opinion because of my feelings of empathy or anger or disgust because I want to affiliate with other people around me and they share that opinion, because of how I was raised. Many psychologists believe rationality is irrelevant for adult moral judgments. I think that's mistaken. I think that's way too strong. I think that there's demonstration after demonstration of how people's rational, deliberative thoughts can actually shift their moral views, lead to a moral decision, lead to moral action, cause people to change their mind and then change the minds of others. I think unless you allow for an important role or rationality, you're unable to explain moral progress or moral change. You're unable to explain why the fact that right now, you and I have all sorts of different views about gay marriage, racism, slavery, then people 100 years ago, even 50 years ago. So I'm a big fan of rationality.

But a lot of my research does address the question of the role of the emotions and our moral judgment and our moral decision making and again, we typically use people's attitudes for homosexuality and gay marriage as a case study. And this is some work I've done with David **** at Cornell University, as well as with other colleagues, and what we do, what we find, is that the emotion of disgust plays a very strong role in one's feelings about gay marriage and about gay people more generally. So we find that people who are disgust-sensitive, so we all have various sensitivity, we're all grossed out by some things and not others. Some of us are more grossed our, are grossed out easier than others. Those of us who are easily grossed out tend to be more morally disapproving of certain human activities, including homosexuality.

Also, you can do this in the lab. So following some work by Jonathan Hite and his colleagues, what we did was, we put people in the lab, we'd ask them questions about all sorts of activities, including their attitudes about gay marriage. For half the people, we'd just put them in a lab. For the other half of people, we evoke disgust. We did that actually by spraying a fart spray in the room, so people get a bit grossed out. Being grossed out makes you meaner, it makes you less approving, it makes you sterner in certain ways.

So, my view on the interplay between reason and emotion and adult moral judgment is it's a complicated and very rich story. But it seems inescapable that our emotions play a role in our moral judgment, even in cases where we might not know this is happening. And even in cases where we'd rather it wasn't happening.

Recorded on November 20, 2009
Interviewed by Austin Allen