Where Explanations End

Today’s piece is a bit different—it’s a short story by Dan Shipper that is a part of the book he’s writing. Read the first five pieces in this series, about the new worldview he's developed by writing, coding, and living with AI; how AI will impact science, business, and creativity; and how tools shape how we see the world. We’re off tomorrow for Veterans Day in the U.S. and will be back on Wednesday.—Kate Lee

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For my money, the West began in an Athenian mansion in 430 B.C. Within it the philosopher Socrates debated the venerated teacher Protagoras about a simple question:

Can excellence be taught?

Not excellence in archery or carpentry—no one doubted that specialized skills could be taught—but the deeper kind of excellence the Greeks called aretḗ: the general excellence that makes a person a good citizen, a good decision-maker, and a fully realized human being.

We know about this debate because it was immortalized by Plato in his dialogue Protagoras, which tells us more or less what was argued:

Protagoras said “yes,” general excellence can be taught. Every moment of a child’s life, he argued, is training in excellence: Through imitation, story, and experience we learn how to live well.

Socrates, the philosopher, said “no.” And he argued it through a new form of thinking: philosophical inquiry. He asked Protagoras to define excellence—was excellence one thing or many? Were justice and courage part of excellence, or something separate?

Protagoras, one of the most famous and well-regarded teachers in Athens, could not define it. Each idea he offered collapsed in self-contradiction—as did his reputation. After all, how could he claim to teach aretḗ if he could not even say what it was?

This debate reminds me a lot of AI. For decades, we followed Socrates—trying to define intelligence, to find a theory of it that would lead to AGI. Then a small renegade group of researchers eschewed theory in favor of a different approach: training neural networks on vast amounts of data. And suddenly real machine intelligence was born.

These systems, in their strange way, are an answer to Socrates’s question about how we can teach what we cannot define. And in their own way they vindicate Protagoras: They show us that excellence can be learned through training, and we can become excellent at things we can’t fully explain.

I’ve always wondered what happened to Protagoras after that night in Athens. I wondered—in the same way we discovered neural networks—whether he figured out how to teach what can’t be defined. And so I wrote a story about it.

When the lamps were finally extinguished in Callias‘s house and the great men had made their way home, Protagoras walked the dark streets of Athens.

For 40 years he had wandered Greece teaching excellence. He had helped craft laws for distant cities and advised Pericles himself. But Socrates’s question haunted him. He could recognize excellence, nurture it, even teach it. But define it? Grasp it in his hands and show another exactly what it was? No.

In the years that followed, Protagoras circled on this question. He gave up teaching in the houses of Athens’s wealthiest citizens. The Peloponnesian War broke out, and the boys he had taught marched off to battle. But Protagoras felt nothing because he saw nothing; the faces of those men were like masks to him, indistinct and abstract.

Eventually, Protagoras exchanged his flowing purple robe for a rough one, as he no longer used his eyes. Eyes in disuse, his sight itself began to fade. Slowly, Protagoras went completely blind.

In 430 B.C., Athens was struck by a plague. The sick and dying lay in the streets. Protagoras sought refuge in a temple of Hermes, god of boundaries, messenger of the gods, guide to the underworld, and protector of the blind. The temple sat at the first milestone from Athens, where two roads met. It was no Acropolis, just a mound of stones—a herma—to mark the junction, with a crude shelter built around it. The shelter had walls of wood scavenged from carts abandoned on the dusty road, and a patchwork roof made of tile and thatch carefully pitched so that rain ran down into collection jars. Merchants met at the herma to make offerings to its namesake god, who protected travelers and businessmen alike, and to exchange goods from far-off lands to be sold in the markets at Athens.

The shelter housed a gang of orphaned children, blinded by plague but still alive, their families killed by the disease that devastated their city. They took offerings from the travelers who passed by, sang hymns to Hermes, and sat all day in the hot, sun-hardened dirt next to the temple.

“By Hermes himself, I’ll pay double the market price. Double!” The high-pitched voice cracked through the herb-soaked cloth covering its owner’s mouth.

The plea was directed at a Phoenician trader who’d set up shop near the temple. In the surrounding darkness, Protagoras recognized the voice as belonging to Callias, the man whose mansion had housed his fateful debate with Socrates.

“Pure white hellebore, from the mountains,” said the Phoenician. His voice was deep and jagged. “I already have a buyer in the city, but if you can pay me now I will forget about him.”

Callias clutched a leather pouch to his chest with shaking hands. For three weeks he’d been trying to buy hellebore root for his granddaughter’s fever. “Yes, but only if you’ll swear they’re real.”

They stood far apart, as plague custom demanded, their words carrying across the dusty crossroads. The morning sun cast their shadows toward the herma, where the blind children huddled, listening.

“And how will I know that what you offer to pay me with is real?” said the Phoenician. “I don’t know you. Why would I risk plague to test your silver with my teeth.”

“The silver is good,” Protagoras said from the shelter’s doorway. “I’ve known Callias since he was a boy.”

The Phoenician turned toward the voice. “Protagoras? The sophist?” A pause. “Then you know about such things. Come, test this silver yourself, and the hellebore too. Your word would be enough.”

“These days I keep my distance.” Protagoras gestured at the space between them, thick with the miasma of plague. “As we all must.”

“A wise man. But without someone to test it, there can be no trade. Not with death in the air,” said the Phoenician as if casually flicking a fly off of his arm. He began to pack away his goods. “Perhaps when the plague passes.”

“When the plague passes,” Callias repeated hollowly, “my granddaughter...”