I have quite an issue with truth and conversations. I'm a scientist but I ended up taking some weird paths. Science is a way of asking questions to the world and of listening to the answers. We will never know everything. But that doesn't mean we know nothing. There's a lot that we already know. However, the evidence is sometimes set aside when making decisions or forming an idea of the world. For example, we already know that climate change is real, but some still deny it. We already know that vaccines work and are safe. But some still doubt about it. That was my first disappointment. Evidence is necessary but not sufficient. This opened up a new path for me. I thought the problem was education. So I left the lab and I turned to teaching. I love teaching. The classroom is one of my favorite places. But there I found the same problem. I was teaching on vaccines and one student said she didn't get vaccinated because vaccines seemed dangerous. My hunch was, "She says this because she doesn't know, if I explain, she will change her mind." I explained to her, but it didn't work. The evidence is not enough. Education is not enough. Second disappointment. This that happened with my student was my first personal experience with post-truth. It's what happens when, although the information is there, it's set aside and emotions or beliefs ensue. With this, another new path opened up. Maybe, it's a communication problem? Given that science is a tool, I used it to study post-truth. I started having conversations with people who don't trust vaccines, while meeting doctors and journalists in an attempt to improve communication on this subject. And there I realized that I had never learned to talk with those who think differently. For example, how do we dialogue when the problem is not the evidence but an ideological disagreement? Experiments show that when people talk only with those who think alike their opinions become more extreme and homogeneous. But in order to have a healthy democracy, don't we need that those who think differently engage in broad, honest and deep conversations? This is far from happening. Every discussion, every disagreement, every conversation looks like a battle between good and evil. Our opinions, instead of being temporary, bridges to communicate with others, are immovable, a ditch that we dig and tells apart those on our side from the others. Dialogue disappears, agreements are impossible, and the world shatters in an explosive combination of aggression and distrust. Can we do something about this? Not all opinions are born equal. Some are weak, or short-lived. Others are intense, or long-lasting. And others become part of our identity. When that happens, any doubt on what we think becomes a doubt on who we are. And that is unbearable. In addition, the need to protect our integrity makes us team up with those in our same situation. This is tribalism. That's why sometimes neither  evidence nor education works. We don't think something, we are that something. (Applause) Let me ask you a question. Did it ever happen to you of going to a meet up with people you don't know and thinking something like, "Mm, I don't know what these people think, I better not talk about this or that"? Did it ever happen to you? Let's see, raise your hand those who lived something like that. Look at you. The harm of tribalism is not only that it creates a climate of permanent conflict but that it also creates silence. Some of us withdraw from the debate, not because we don't have opinions or we don't care about what happens. We are not halfhearted. It's the atmosphere of aggression, it's things not moving forward, it's fear, exhaustion, and the social punishment of dissent. It's for one or more of these reasons that we leave conversations in silence. A loud silence. And so, the inability to dialogue causes the number of voices to go down. Until there is only one left, sometimes. Silence is confused with agreement. And the illusion of consensus is created. Because one opinion is heard, there seem to be only one. And then any other opinion is not only different, but dissonant, alien, and must be eliminated. In general, we think of censorship as a power which bans from above. But there is another, more subtle way. Censorship from below. Through tools of social discipline, such as raising the tone of the fight, it makes us withdraw. This is a threat to free expression. And it makes me think that  it's also a problem for democracy. Both in our small environment and on a large scale. It would seem then that we only have two options. Whether we share our ideas despising those who don't think alike, or we shut up. And by doing that, we give up control to those who speak up. But this is a false dilemma. There is another option, but we need to make it evident, because it is hidden in this sea of tribalism. We can have defined positions, even very intense ones, without riding on the dynamics of intolerant speech. It's one of the things I learned when talking to people who doubt vaccines. To break tribalism, to find more voices, to break this "friends or foes" dynamics, I propose to distinguish between what we believe in and how we believe it. And if we make this "how" non-tribal, we can raise our opinions without allowing what we think to become who we are. The nuances reappear and conversations become possible. And from that point we can build consensus which are the product of agreements, despite our differences. However, when I talk about these ideas I usually get some criticism. It seems that in order to avoid conflict I suggest that we let consensus happen anytime. No, that is not what I mean. If we don't express ourselves because we feel alienated or expelled we are not taking part in decision making. But we all live with the consequences of those decisions. So, since we do care, we need to talk. But if we don't want to talk in this hostile atmosphere because it's exhausting and we see that it leads nowhere, let's try to move past tribal mode. Beyond what we think. We may have more in common with those who think differently yet want to talk, than with those who share with us same opinions but are intolerant. (Applause) They also usually tell me that there isn't much we can do on the individual level to move past tribal mode. But I think there are some very concrete things to do. And I have three suggestions that could help. First, look for pluralism. Promote it actively. So dissent becomes visible and this is important because only if we include dissent we can achieve a true consensus. For this to happen we need to be able to talk without feeling that we are socially punished. But it also requires listening to voices we don't like. The moment to defend freedom of expression is now. Taking care of it is easier than recovering it. Learn to have better conversations. To find better ways of disagreeing. A conversation is not waiting for our turn to talk, trying to impose our ideas by force or insistence. It's about listening to understand others. Without listening there's no conversation. Third, separate ideas from people. Under tribalism, attacking an idea makes the person feel threatened because they feel attacked as a person. But how are we going to improve ideas with that attitude? We need to discuss them, so that the best survive. People deserve respect. Ideas have to earn it. Humans are inventors. At some point, somewhere, we invented the idea of sitting by the fire to talk. And at some point, both conversations and fire look alike. Both are always in between two dangers. The danger of dying or growing out of control. It took us time but we learned to handle fire. We learned to keep it alive so it doesn't go out. And to handle it so it doesn't destroy us. Maybe, it's time to learn to do the same with conversations. Thank you. (Applause)