Chapter Fifty: Arabic Numerals

“What is the use of mathematics?”
It was Master Mo’s first time teaching a class, and he was a little nervous. Fortunately, apart from Li Gaoming, the others were all familiar faces, which helped Mo Dun relax quite a bit.
“For the exams?” Cheng Chumo raised his hand high and uttered a great truth.
“Er…” Mo Dun was speechless.
“For keeping accounts!” Zu Mingjun suggested a practical purpose.
“Accounting is indeed a major use of mathematics,” Mo Dun nodded.
“But the uses of mathematics do not end there. Once you have learned mathematics, as a general, you can calculate the speed of your army’s march, the time it will take to reach the battlefield, the amount of provisions required, and even estimate various aspects of the enemy’s forces. With such calculations, how can such a general not win his battles?
As a minister, you can compute the nation’s taxes and expenditures, uncover corruption through audits, and govern the state with reason. Ordinary folk can keep accounts and record household spending. Even the street vendors must master arithmetic by themselves. Mathematics pervades everyone’s life.”
“We deal with mathematics every moment of every day. Mathematics is important—I love mathematics more than any other subject! Today, I want to teach you not only mathematics, but the very spirit of mathematics.
In mathematics, every number is fixed, unchanging. One plus one equals two, never three or any other number. Mathematics is a realm of cold, precise numbers—strict and exact, revealing the naked truth. You may doubt anyone and anything in this world, but I urge you to trust mathematics. All people may deceive you, but mathematics never will. Once you master mathematics, you gain the power to discern the truth.”
Mo Dun’s words left everyone thoughtful, especially Li Gaoming, whose eyes sparkled with insight.
Even Qin Huaiyu and his two friends, who had only intended to idle away the time, sat up straighter and listened attentively.
“The mathematics of the Mo family is different from the arithmetic you learn from the Ten Mathematical Classics! Its entire foundation lies in these ten numerals: zero, one, two, three, four, five, six, seven, eight, nine.”
Mo Dun picked up a charcoal pencil and wrote these ten numbers on a wooden board.
Seeing his hand covered in black dust, Mo Dun silently resolved to introduce chalk as soon as possible, since the process was so simple.
“We’ve learned these before!” Yuchi Baolin remarked with confusion.
“Have you?” Mo Dun smiled faintly. “Then what about these ten figures?”

Mo Dun wrote beneath the board: “0123456789.”
“Are these numbers too? They look like scribbles!” Everyone was baffled by the crooked shapes of the Arabic numerals.
“Mo Dun, have you started learning witchcraft? These look like magical runes!” Qin Huaiyu joked.
“These are numerals, but from India, aren’t they?” Li Gaoming suddenly spoke.
Mo Dun looked at Li Gaoming in surprise, not expecting him to know this. Indeed, these were Indian numerals, but it was Arab merchants who had spread them around the world, leading to their later name, Arabic numerals.
“These are indeed Indian numerals. Brother Gaoming, your knowledge is impressive. These are the very essence of mathematics the Mo clan painstakingly traveled to India to learn!” Mo Dun shamelessly credited the Mo family.
Mo Dun then wrote out a few numbers in Chinese characters and then in numerals, explaining their meaning. All five present had a foundation in mathematics and quickly understood.
The difference was striking: Arabic numerals were vastly superior for large calculations, simple to learn and immediately clear.
“This is just too convenient!” Qin Huaiyu was thoroughly interested. If all math were this easy, he would have mastered it long ago.
“The ancestors of the Mo family are truly admirable. I heard that several years ago, a high monk named Xuanzang vowed to travel to India for the true scriptures, but it seems your ancestors had already brought back the true essence of mathematics from India,” Zu Mingjun exclaimed in delight.
“Er…”
Even Mo Dun, thick-skinned as he was, blushed a little and tacitly accepted the praise, silently apologizing to Xuanzang for sharing in his glory.
Mo Dun then briefly taught the five students addition and subtraction, leaving them amazed—compared to the methods in the Mathematical Classics, this was far too convenient.
Zu Mingjun, especially, was completely absorbed, lost in the pleasures of calculation.
“That’s all for today’s lesson.” Mo Dun breathed a long sigh of relief, interrupting the reluctant practice of the five, and ended the day’s class.
They reluctantly put down their goose-quill pens, having discovered that writing Indian numerals with these pens was far quicker and neater than using brush pens, which never seemed to write them well. They all switched to goose-quills—perhaps their first expansion.
“Brother Mo, your generosity in sharing the Mo family’s mathematical secrets so freely is deeply appreciated,” Li Gaoming said sincerely.

Zu Mingjun also expressed his gratitude repeatedly. By comparison, the Mo family’s mathematics far surpassed his own family’s ancestral methods. The Indian numerals alone left Zu Mingjun with no thought of rivalry.
“Not at all, not at all,” Mo Dun replied modestly.
After all, the six of them were still young, and without so many formalities, they quickly became fast friends and enjoyed themselves greatly.
Before they knew it, it was time for dinner. Mo Dun invited Zu Mingjun and Li Gaoming to stay for the meal. As for Qin Huaiyu and his two friends, they were incorrigible guests who simply wouldn’t leave.
“Well, I won’t decline! I’ve long heard that Brother Mo’s invention, the steamed bun, is incomparably delicious. Mo family cuisine is always unique,” Li Gaoming said heartily.
“Then you’re in luck. My Uncle Yu is here today—his fish dishes are second to none. It’s said that back in the army, even His Majesty once praised his cooking,” said Mo Dun.
“Oh! Then we must truly taste it,” Li Gaoming laughed.
Since Li Gaoming had agreed to stay, Zu Mingjun did not stand on ceremony and stayed as well.
“The fish is ready!” Master Yu brought the dishes to the table: one dish of fish with pickled greens, one braised fish, one steamed fish, and several small side dishes. Each person received a bowl of steaming rice, though three of the bowls were conspicuously large—clearly reserved for Qin Huaiyu and his two friends.
“Please enjoy, young masters!”
After Master Yu left, Mo Dun pulled over a chair with a back specially made for him by Old Zhang, inviting the others to sit. The table was the Mo village’s characteristic round table, with no distinction of rank or position.
“These tables and chairs are quite unique!” Li Gaoming observed, leaning back to find the chair supported his lower back perfectly—it was very comfortable.
“There are no strict rules in the Mo family—comfort is what matters,” Mo Dun replied. He was never comfortable with the Tang custom of kneeling at meals; outside, he had no choice, but in the Mo residence, he had changed everything to tables and chairs, using family tradition as an excuse so it wouldn’t seem odd.
As the host, Mo Dun was the first to pick up his chopsticks, take a piece of fish, and begin the meal.