I have been invited to two debates in the next few weeks in Barcelona, to discuss about secession versus federalism in the relations between Catalonia and Spain. And I am active in the creation of opinion favourable to a federal solution (as the faithful reader has observed). There is an election to the Catalan Parliament on September 27th and there will be many more debates with more important people, as there are always debates in democratic societies around elections. But now that I have been invited (I am not a candidate, just a committed citizen who has friends willing to risk their reputation by inviting me to speak), although not for the first time, to two of them, I wonder whether they are any useful. They are no doubt fun and exciting for me, but I wonder what are the odds that I will convince any one of my ideas, or that any one will convince me to change my mind on anything. Empirical work in social psychology is somehow divided on this. On the one hand, it is well known that through the confirmation bias, we first develop our judgement by intuition, avalilability, social pressure or self-interest, and only afterwards we use reason to justify it, meaning that reasons do not determine judgement. But on the other hand precisely because of confirmation and other biases (such as conformity or herd behaviour), we do need devil's advocates and some mental exercise to put our prejudices always on the spotlight. On issues so emotionally charged such as identity politics, it is really difficult to find someone changing their mind as a result of debates, many of them being just status or reputation battles. But opinions evolve, and perhaps, just perhaps, something that one day is said somewhere by someone has an effect some time later, or this something contributes to avalilability or social pressure. And it is probably healthy to talk to people with different ideas. Better this than resolving the issues by other means. So let's debate.