In cheerful contrast, at the classroom’s other end, the young orangutan Virgil was stimulating the minds of his three ape pupils. He was trying to exercise their brains with argument, not fill them with facts. The dialogue was quick tempoed.

“But, Virgil, can we alter destiny? Can we tamper with time?”

Virgil’s smile was mischievous. “Accept my premise, and I will prove it logically.”

“What premise?”

“That the legends are true—that Man learned to travel not only faster than sound but faster than light as well.”

“All right, we accept the premise.”

“Then imagine a musician giving a live broadcast from what was once London to what was once New York on a Wednesday. He then travels faster than light from London to New York, where he arrives on the previous Tuesday, listens to his own broadcast on Wednesday, dislikes its quality intensely, and travels back faster than light to London in time to talk himself out of giving the broadcast in the first place.”

The chimpanzees and the orangutan shouted with laughter at this dubious but invigorating idea.

On the other side of the room, Teacher heard the happy laughter and envied it; that was what teaching should be. He sighed and went on mechanically scrutinizing and stacking on the desktop the parchments that the last of the chimp and orangutan children were now submitting for his inspection, “That’s very good, Mirko. You’re dismissed.”

Cornelius was the last of the chimps to present his parchment. Teacher looked it over carefully. “Good, Cornelius . . . Oh, there’s a mistake. You’ve written a ‘B’ for the second ‘P.’ ‘APE SHALL NEVER KILL ABE.’ ” He smiled jovially, “Who’s Abe?”

There was a pause. Then Cornelius said softly, “Teacher, have you forgotten your own name?”

Teacher was startled—and then touched. His eyes became moist. His voice fell to a whisper, and he mused, almost to himself, “So many people call me ‘Teacher,’ I’d almost . . .” He smiled at the chimp. “ ‘Ape shall never kill Abe.’ Thank you, Cornelius. That was a very kind thought.” He pulled himself together with visible effort. “You’re dismissed.” Cornelius trotted out.

He stood up and looked toward the back of his class. “Gorillas! Are you done?” He stared at them as firmly as he could; they were so much like children; discipline was all they understood. It was a shame their bodies had matured before their minds. With their incredible strength to force things to their will, they had no incentive to learn; they could accomplish what they wanted by the most direct—and brutal—method.

The gorillas were hunched, motionless yet menacing, on their back-row benches. Aldo rose from his place and slouched insolently toward Teacher. He slapped his parchment on the desktop beside the others.

Teacher picked it up and scrutinized it. “General Aldo, with respect, this is barely legible and will have to be written again. Your capital ‘A’ leans over like a tent in a high wind, and your ‘K’ is . . .”

Aldo curled his lip. Glaring at Teacher, he deliberately took Cornelius’ parchment from the top of the pile and began to tear it into shreds.

Teacher shouted at him, agonized, “No, Aldo! No!”

Abruptly, every ape in the room froze, shocked into hostility. Aldo turned apoplectic. The gorillas sprang to their feet in menacing unison. Virgil, appalled, raced across the schoolroom floor. “Teacher!” he cried. “You’ve spoken the unspeakable! You’ve said ‘No’ to an ape!”

Teacher went pale, shocked with the realization of what he had done.

“Teacher!” said Virgil. “You know better—you know why a human must never, never, say ‘No’ to an ape. In all our years of slavery to men, the word ‘No’ was the one word apes were electrically conditioned to fear. Caesar has forbidden men to utter it ever. An ape may say ‘No’ to a human. But a human may never again say ‘No’ to an ape!” He stepped in closer and whispered, “Tell them you’re sorry, Abe, and go home while you still have a home to go to. I’ll try to put in a word for you with Caesar.”

Teacher nodded slowly and turned to the gorillas. “I . . . I’m sorry. The writing you destroyed was by Caesar’s son. I . . . did not want you to suffer Caesar’s anger.”

Aldo snarled at the name. “What do I care for Caesar’s anger? Let me give you a taste of mine!”

The big gorilla lifted up a block of wood and hurled it at Teacher’s head. Taking their cue, the other gorillas began to run joyfully amok, roaring and screaming. They overturned Teacher’s desk and ripped up the papyruses. And then they headed for Teacher.

Teacher ran from the classroom. The gorillas boiled after him like bees swarming out of a hive. He lurched out into the street, stumbled, caught his footing and ran. The gorillas chased after him, and the rest of the students, seeing the excitement, came tailing after.

Teacher panted as he ran—he wasn’t used to this kind of exercise—his lungs ached from the effort; he charged through stalls of fruit and vegetables. The gorillas came barreling after, upsetting baskets and tables. Aldo was in the lead, shouting and roaring. The shoppers and stall-tenders screamed as they leapt out of his way.

Teacher dodged and whirled, around a house, down a street. There, ahead of him! There was a work area where humans were plaiting screen walls for houses. Maybe he could hide there! But the gorillas had already seen him. They came crashing through the screens after him.

Teacher tried to hold onto his glasses as he ran. He took off again, this time in a different direction—toward Caesar’s house. Caesar would help him!

But he wasn’t fast enough. Aldo came roaring down on him like a freight train and threw him roughly to the ground, pushing him into the dirt.

Grinning fiercely, Aldo drew his sword from his belt. It was broad and flat and short. He raised it high over his head.

Teacher tried to raise one arm in protest. Apes and humans alike gasped in shock.

And then someone, an ape, cried, “Stop!”

All heads whirled to look—it was Caesar, standing in his doorway. He was a tall, strong chimpanzee; he had the bearing of a leader. Just behind him stood MacDonald, his chief human adviser.

The gorillas stared at Caesar. Aldo glared sullenly at him, his sword still raised over Teacher.

Caesar stepped down from the doorway, his stare fiercer than Aldo’s. “I said . . . stop . . . Aldo.”

Their eyes locked. Aldo burned with a fierce red anger, but Caesar’s quieter strength was more effective. Aldo averted his eyes. He looked around for support, but there was none from the other gorillas; they were too thoroughly cowed by Caesar’s authority. And there was certainly none from any of the chimpanzees and orangutans in the crowd; they were eyeing the gorillas with cold disdain and Caesar with love and respect.

At last, slowly, Aldo lowered his sword. But he waved in the direction of the Teacher, shouting his frustration. “He broke the Law! With his own mouth he broke the First Law!”

Caesar seemed to grow. “I am the Law,” he said sternly. “And if I find that he has broken it, I shall pass judgment. What has he done?”

Virgil pushed forward through the crowd. “I can tell you. I was there.”

Caesar turned to him, his tone softening, “Yes, Virgil . . .?”

“I was there,” Virgil said breathlessly; he too was still panting from the chase. “Teacher only . . . only . . . reverted to type under provocation. He spoke like a slave master from the old days of servitude, He spoke the negative imperative used for the conditioning of mechanical obedience.”

Caesar smothered a smile. MacDonald grinned broadly. Caesar said, “Put that in words which even Caesar can understand.”

“He said, ‘No, Aldo, no!’ ”

The crowd gasped at that, the apes in anger, the humans in fear.

MacDonald stepped forward and began to help Teacher up. “Teacher, you’re old enough to be well aware that ‘No’ is the one word a human may never say to an ape, because apes once heard it said to them a hundred times a day by humans.”