Journal/AI & Society/What Happens When You Debate an AI

What Happens When You Debate an AI

In 2019, Harish Natarajan stood on a San Francisco stage and argued against IBM's Project Debater. What he learned that night says more about persuasion than it does about technology.

Written by
Harish Natarajan
Published
May 19, 2026
Reading time
6 minutes
Category
AI & Society

The theatre was full. It was a San Francisco crowd, filled with engineers, entrepreneurs, and true believers, convinced that they were watching the future arrive. At the front of the stage stood a black rectangular column, human height, with a single blue oval glowing near the top. I had been told what IBM's Project Debater could do. Hearing it was something else entirely. Its first words on stage were simple. "Welcome to the future."

IBM had a habit of setting itself seemingly impossible challenges. In 1997, Deep Blue beat Garry Kasparov, the reigning world chess champion, at his own game. In 2011, Watson defeated two of the greatest Jeopardy champions of all time. A week after that victory, the company asked its researchers what should come next. Noam Slonim, working out of IBM's lab in Haifa, proposed something that had never been done. Build a machine that could debate. Not answer questions. Not optimise moves. Argue with a human opponent, on a topic it had never seen before. Project Debater was the result. When it spoke, it was fluent, structured, and relentless. It opened with a joke. It cited peer-reviewed research. It anticipated counterarguments. For someone who had spent years making arguments, it was genuinely impressive. And genuinely strange.

But it had a flaw that no amount of data could fix. Debate is not just an exercise in accumulating the strongest evidence. It is an exercise in working out what will persuade the specific people sitting in front of you. Project Debater could identify what was true. It could not read a room. It piled argument upon argument, each one logically sound, none of them calibrated to the audience's doubts. The philosopher Arthur Applbaum, reflecting on the debate, asked if hearing every argument on a topic actually helps us think more clearly about it. It does not. Hearing every conclusion is not the same as being helped to reason. The machine had mistaken comprehensiveness for persuasion. They are not the same thing.

But that was 2019. That was before large language models existed. Back then, AI could only retrieve pre-assembled arguments rather than generate original ones. Building an AI debating system today would produce something categorically different. Claude, for instance, can identify the weakest point in an opposing argument, and do so across any topic, in seconds. It can deploy persuasive rhetoric. Used well, it would make anyone faster, sharper, and capable of arguments they would never have thought of. A modern AI debater would not be perfect. But it is impossible to believe it would not be a far more serious challenge than what I faced that evening.

But can an AI learn what actually persuades people? Chess suggests artificial intelligence has left humanity behind entirely. Magnus Carlsen, the strongest player in the history of the game, has said that he has no chance against his phone. The gap between the best human and the best chess engine is not close; it is not even interesting. But chess has a feature that debate does not. There is an objective measure of who is winning. And the same machine that would humiliate Carlsen cannot reliably pick up the pieces afterwards. A toddler manages it without thinking.

Persuasion looks more like picking up the pieces than playing the game. Knowing the best justified argument is not the same as knowing which argument, delivered how, will shift this person's view. That gap between correctness and persuasiveness is where human debaters have always lived. Whether AI can close it is unclear. And even if it can, would it matter? When I stood in that hall and heard the machine speak, part of what the audience was responding to, I suspect, was me. Not just the argument. The fact that a person had made it. Whether that changes with time, or whether something about knowing the source is a machine keeps us resistant, is a question the technology will eventually force us to answer.


Filed under: AI & SOCIETY · ESSAY
First published: May 19, 2026

Harish Natarajan

Debate Champion

Harish Natarajan is one of the world's leading competitive debaters. In 2019, he became one of the first people to publicly debate IBM's Project Debater at its live demonstration in San Francisco.