A HUMAN HISTORY OF MATHEMATICS凿构周期律 · 数学鑿構週期律 · 數學 · 01 / 25
Counting, Measuring, and Keeping Accounts
计数、丈量与账目
計數、丈量與賬目
Clay could remember sheep, grain, and days of work. What it remembered depended on who was holding the stylus.
泥板替人记住了羊、谷物与工日。它也开始决定,哪些事情可以进入总账,哪些人只能留在账外。
泥板替人記住了羊、穀物與工日。它也開始決定,哪些事情可以進入總賬,哪些人只能留在賬外。
In this essay篇内目录篇內目錄
1. A number still belonged to something
Three people have a flock of sheep to divide.
They may not need to write down a single numeral. Drive the animals into three groups, move a few from one group to another, and keep going until everyone is satisfied. Perhaps nobody can say afterward exactly how many sheep they took. That afternoon, at least, nobody objects.
Now change the arrangement. Part of this year's flock is owed to an institution, and the amount depends on last year's shortfall. The animals are scattered among several villages. The person collecting them is somewhere else. Some must be converted into an allowance of grain at a rate set by a third party. Three roughly equal groups will no longer do. Somebody needs a record that another person, in another place and another month, can read in the same way.
That is the sort of work the earliest surviving tablets were doing.
To see what made their notation unfamiliar, imagine two records from Uruk around 3300 BCE. This is an illustrative comparison, not a claim about two identifiable museum objects. One records livestock; the other records a quantity of barley. We might expect to recognize the same number wherever it appears. The scribe could not simply make that assumption.
Late-fourth-millennium scribes used several numerical systems. Discrete objects, including people and animals, belonged to one; grain capacity to another; land area and other measurements had their own conventions. Certain products and rations required further distinctions. These were not merely different fonts for a single universal notation.
A numerical sign could therefore take its value from the kind of quantity being recorded. Copy it unchanged from one system into another and you might no longer have the same amount. Before reading the number, you had to establish what was being counted or measured.
This does not mean conversion was impossible. Relations between units could be learned and used. It means the notation did not carry everything a later reader would need inside itself. The commodity, the unit, and the activity still helped determine the reading.
A tablet could consequently lose some of its intelligibility when it left the setting that produced it. The original writer knew what everyone in the room knew. There was no need to state it all. An archaeologist confronting an unprovenanced object may be trying to recover precisely what the scribe had been able to leave unsaid.
It would be a mistake to call this simply primitive. The systems grew close to the things they served. Capacity units were related to containers, area units to ways of surveying land. Counting a shepherd's animals and receiving grain into a storehouse were different activities. They had accumulated different working conventions.
Specialization could also be convenient. A storekeeper who spent his life measuring grain did not always need notation suited to counting livestock. A local practice could leave out what it did not use. The difficulty became more visible when records from different activities had to be brought together.
Cities made that happen more often. Storehouses, temples, work crews, and continuous deliveries created obligations that could not all remain within separate little worlds. Who owed what had to be compared. Much later, an abstract calculating layer would help connect quantities expressed in different units. That development took more than a thousand years; it did not arrive with the first numerical tablet.
The oldest records already had a clear practical destination. So much received. So much still outstanding. So much issued to someone else.
They were not being written for us. They were being written so that somebody could check next month.
2. Most of the earliest writing was an account
The proto-cuneiform corpus is usually discussed in terms of roughly six thousand tablets and fragments, about five thousand from Uruk itself, with others from sites such as Jemdet Nasr. In the conventional chronology, these materials span approximately 3350–3000 BCE. Such totals describe a scholarly corpus, not a complete inventory of everything once written.
Hans Nissen's familiar classification put economic and administrative documents at about 85 percent and non-administrative material, principally lexical lists, at about 15 percent. The lists became more prominent in the later phases. In the earlier material, administrative recording is more overwhelmingly dominant still.
So, among the earliest written objects we actually possess, accounts are not a narrow majority. They constitute most of the evidence.
These were not account books in the modern sense. A record might combine a quantity sign, a commodity or personnel sign, and a mark for an institution or individual. The script did not yet freely reproduce all the possibilities of spoken language. Quantities and categories were often more legible than anything we would call a sentence. It was particularly good at saying how much of something had gone to someone.
Even a possible personal name reaches us through this environment. A pair of signs conventionally read as Kushim recurs on eighteen Uruk tablets associated with barley and brewing materials. One records grain handled over thirty-seven months. Whether Kushim names a person, an office, or an institution remains uncertain. A common reading makes it a person. If that reading is right, one of the earliest recoverable human names belongs to someone on a barley account.
But the percentage needs a brake attached to it. Eighty-five percent of the surviving corpus is not the same as 85 percent of everything people originally wanted writing for.
Clay preserved certain activities exceptionally well. A discarded tablet could dry out; a building fire could harden it. Other practices relied on wood, fiber, spoken instructions, temporary marks, or wet clay rubbed smooth and used again. They did not all have the same chance of entering an archive, much less a modern collection.
Administrative demand was central to the environment in which writing took shape. That is a strong historical claim. Accounting was the sole reason anyone invented writing. That is a different claim, and the evidence does not carry it.
Nissen, Peter Damerow, and Robert Englund connected early writing with the increasingly complex management of resources by urban institutions. Their account identifies a setting and a set of pressures. A neat origin story supplies a single intention. No inventor's statement from 3400 BCE survives to settle that difference.
The small clay objects usually called tokens pose a related problem. Cones, balls, disks, hollow clay envelopes, and impressions on their surfaces are real archaeological finds. Denise Schmandt-Besserat proposed a long developmental sequence: simple tokens stood for quantities of goods, more elaborate tokens represented a widening inventory, tokens were enclosed in clay envelopes, impressions recorded them outside, and eventually two-dimensional marks replaced the three-dimensional objects. Writing emerged from that process.
There is real material beneath the proposal. Some envelopes really did contain tokens. Yet resemblance in shape does not, by itself, establish continuity of use and meaning across thousands of years. Many objects lack a secure accounting context. Their shapes do not map onto the earliest written signs as consistently as a strong version of the theory requires. They may have served several purposes.
A more limited account is easier to defend: some tokens, sealings, and numerical impressions belong to the history of accounting technologies. A unified prehistoric token system, stable in meaning over millennia and capable of yielding the signs of writing one by one, is not an established consensus.
The difference matters because origins are unusually hospitable to tidy stories. A sequence of objects can look like a sequence of intentions. Those are not necessarily the same sequence.
3. A person becomes a workday
By the Third Dynasty of Ur, the documentary world is much larger. Known administrative texts from this period number on the order of 120,000.
One revealing form is the balanced account. Start with what should have been delivered or accomplished during a period of responsibility. Subtract authorized expenditures, losses, and completed work. Establish the remainder as a surplus or deficit. Add dates, the responsible person's name, and whatever the accounting procedure requires.
The decisive operation is conversion. Labor becomes workdays. Agricultural tasks, textile production, grain, and wool can be related through prescribed rates of production. At places such as Umma, groups were organized under foremen or supervisors. The administration wanted more than a head count. It wanted to know how much labor this group was supposed to deliver.
The person at the center of the account was therefore often the supervisor.
Once labor had been converted into an accounting unit, something else became harder to see. One worker was ill today. Another worked more slowly. Another had been given the heaviest part of the job. A total expressed in workdays did not necessarily deny these differences; it did not necessarily have a place for them. Subsequent arithmetic could operate on the figure without encountering the people again.
A group of records from years 37–40 of Shulgi's reign follows hundreds of female workers and their labor and grain obligations under Lu-Urub, son of Minar-ni. Whatever the uncertainties of reconstructing the institution, the supervisor was not merely someone taking attendance each morning. His name could function as a continuing point of administrative responsibility.
A deficit might carry forward into the next period. A surplus might be credited. The next balanced account could absorb the previous one. The name and the number could remain attached across successive years.
Supporting records lay behind the total: receipts, sealed documents, and smaller acknowledgments retained for checking. Ur III accounting even left evidence of containers used to keep these supporting tablets. A balanced account was not necessarily just one tablet. It could be one tablet resting on a basketful of others.
Here an attractive claim sometimes outruns the records. We are told that, when a worker died, an unfinished labor quota passed to the family. There are records of deaths and replacements. There are provisions for dependants and orphans. There are supervisors' deficits carried forward. But placing those facts next to one another does not produce a tablet stating that a named dead worker's outstanding workdays became a named relative's inherited debt.
What the evidence securely shows is the persistence of a deficit in an account. The further claim about the hereditary transfer of an individual labor obligation needs direct evidence of its own.
It is easy to miss the step because the extrapolation seems so plausible. A system capable of reducing living labor to a number might also be capable of passing the number to a son. But what an arrangement could do is not identical to what we know it did.
The supervisor's responsibility needs a similar qualification. An administrative account in his name does not automatically establish personal, unlimited liability in a later legal sense. Was Lu-Urub expected to cover every deficit from his private property? The documents do not give us enough to say that. They tell us whose son he was. They do not provide an inventory of his home.
Even without the stronger claims, the change is considerable. An administration in southern Mesopotamia could take hundreds of people, a year of their effort, and the grain they consumed, convert them into comparable quantities, and place the result beneath a responsible person's name.
The calculation became easier to carry. The lives it represented did not become equally easy to carry with it.
4. The layer where the calculation happens
Another development becomes visible toward the end of the third millennium, particularly in Ur III practice. Scribes increasingly converted concrete measurements into abstract sexagesimal place-value numbers, calculated there, and converted the answer back into the appropriate units.
Two developments should not be collapsed. Counting systems in which sixty mattered already existed at Uruk. A place-value notation in which the position of a sign could give it different powers of sixty became clearly established much later. It entered practical calculation in the late third millennium and reached a mature form in Old Babylonian schools.
Tables made that abstract layer usable.
A standard reciprocal table did not list every integer from one to fifty-nine. It concentrated on numbers whose reciprocals terminate in base sixty, often in some twenty or thirty entries. Other divisors required approximation, decomposition, or another procedure. Multiplication tables supplied products for a chosen number. Metrological tables connected customary units of length, area, capacity, and weight with the numerical system.
A central practical move was to replace division with multiplication by a reciprocal. Find or remember the reciprocal, then multiply. The tables were not merely helpful appendices to a technique that already existed independently of them. They were part of the technique.
For a student, knowledge and memory were closely joined. Learn the table and a class of divisions becomes possible. Fail to learn it and the written numbers sit there waiting. Repeated work on clay was one way to put the procedure into a person's hands and head.
The notation still left something outside the signs. Early place-value writing ordinarily lacked a fixed radix point and the later forms of an internal zero placeholder. The same written sequence might need to be read at scales differing by sixty, by 3,600, or by a fraction of those amounts. Units and context supplied the scale.
That absence should not instantly become a story about constant mistakes. Identifying a particular ancient error as the necessary result of a missing zero, rather than a misplaced sign or another copying problem, would require evidence. The limitation of the notation is visible; a particular failure cannot simply be inferred from it.
The figures handled relative numerical relations. A trained reader supplied the order of magnitude and the connection to grain, silver, or a daily ration. This was not an entirely self-sufficient writing system. It worked with a person beside it.
Nor did standardization mean that a king abolished all customary units overnight. Capacity, weight, length, and area continued to have distinct units. What became more unified was the layer at which calculation took place. Conversion tables were the passage between that layer and the things being measured.
The phrase Shulgi's reforms is convenient for the wider standardization of administration, taxation, labor, and measurement during his long reign. It should not make us imagine a surviving modern-style metrology act, with a royal decree defining every unit relation line by line. Much is reconstructed from the documentary practices that became consistent.
Shulgi's hymns offer something different. In one, the king presents himself as having studied scribal learning, Sumerian and Akkadian, calculation, addition, subtraction, and accounting. Other praise poetry likewise celebrates his learning. Yet the surviving copies are chiefly Old Babylonian school manuscripts, written roughly two or three centuries after his lifetime.
They may preserve earlier court traditions. They cannot function as an independently verified school record. Their secure subject is the image of learned kingship and the value attached to it.
Still, there is something worth noticing even at that level. A king could be praised for knowing how to keep accounts.
5. What survived in one house
At Nippur, a building known by its excavation label, House F, yielded roughly 1,425 tablets and fragments. More than nine-tenths were school material. Unlike so many mathematical tablets bought without a recorded provenance, these objects could be related to actual rooms and archaeological deposits.
The tablets themselves show something of the work. On one common type, a teacher's model occupies a portion of the front and a student's copy sits beside it. The reverse may preserve longer passages or earlier lessons. Small round tablets can place a short model beside its repetition. Student areas were often wiped and reused.
A cheap teaching surface was an expensive loss for the historian. A child could smooth away a mistake and start again. What the child first wrote, how it went wrong, and how many attempts preceded the surviving copy may all have vanished in that gesture.
The objects also differed in how a person could hold them. Yale's round tablet YBC 7289, about eight centimeters across, fits in a palm. British Museum tablet BM 13901 measures about 19.4 by 11.7 centimeters: a more substantial surface for the hands or a table. Wet clay could be corrected; dry clay was less cooperative. Crowded signs, erasures, and recutting preserve some of that negotiation with the material.
Scholars including Steve Tinney, Eleanor Robson, and Niek Veldhuis have reconstructed sequences of instruction from tablet types, combinations of texts, and directions of copying. Making wedges and individual signs led into syllables, personal names, and organized word lists. More complex lexical work, metrology, numerical tables, and literary copying followed or overlapped.
This is a reconstructed curriculum, not an ancient timetable recovered intact. A pupil might repeat, skip, or pursue several things at once. Nor can one house stand without qualification for every school in Babylonia. Robson has been particularly careful about that limit.
School literature brings us closer to a pupil's day, but in a different way. In the composition usually called Schooldays, a student goes to school with a tablet, recites, eats, prepares more work, and returns home to repeat the day's lesson to his father.
Next morning, the teacher finds something missing. The child is beaten.
More beatings follow. The official in charge of the work strikes him; the reason is lost in a damaged passage. Another objects to his talking. Someone else complains about the position of his head. A drawing supervisor asks why he has left his place. The gatekeeper asks why he has gone outside. Another complaint concerns an object whose name is missing. The Sumerian-language supervisor catches him speaking Akkadian. His own teacher dislikes his handwriting. The sequence accumulates punishments until the day seems to contain little else.
That evening, the father invites the teacher home, gives him food, beer, and gifts, and the teacher eventually praises the boy.
The scene almost makes checking it feel unnecessary. That is precisely when the distinction matters: we are reading school literature, not a disciplinary log. The composition belongs to the Old Babylonian world and may draw upon recognizable practices. Its comic or satirical accumulation does not prove that every school operated this way every day.
The tablets independently support a less dramatic picture. Teachers supplied models. Pupils copied them. Work was checked and corrected. Advanced pupils copied literary compositions, including texts about being pupils.
At Ur, another house, given the modern excavation address No. 7 Quiet Street, yielded more than two thousand documents and exercises associated with Ku-Ningal and his family. Calling it simply the home of a hereditary family of professional scribes smooths away important distinctions. Ku-Ningal and several sons had priestly roles. Teaching within the household is well supported; reducing the family's occupations to scribal employment is not. The seal of his son Ur-Nanna gives him religious and archival responsibilities.
There was strong family continuity without evidence of an entirely closed legal caste. Literacy, collections, contacts, and offices could accumulate in a household and give its children an obvious advantage. That does not mean every title was hereditary in exactly the same way.
Nor is there a single salary scale for the profession. Grain, wool, land income, rations, and the privileges of office might all contribute. The prestige of scribal learning cannot establish the prosperity of every minor copyist.
It is tempting to end with an encouraging story about gifted poor children finding a ladder into a different life. The surviving student records do not allow that story to become a general fact. They disproportionately reveal families already connected to administration and temples. The chances of an ordinary farming family's child entering advanced scribal education cannot be calculated from them.
We can see the lesson. We cannot see everyone who was missing from the room.
6. Problems that lead to no payment
BM 13901 contains four columns and about twenty-four problems involving sides and areas of squares and rectangles. Its acquisition did not preserve a secure archaeological findspot.
Read the problems as a sequence and three features stand out. They are arranged by difficulty. Operations return in altered forms. The chosen numbers are exceptionally accommodating.
That arrangement is already a kind of invention. A grain account does not naturally generate a second exercise slightly harder than the first. Somebody has to identify where a learner may stumble, then devise problems that expose and vary that step. The object in the author's mind is no longer only a field. It is a difficulty in another person's understanding.
Such problems commonly wear the clothes of administration: fields, bricks, canals, workers, silver, grain. Those were familiar objects in the scribal world. Their appearance on a tablet does not prove that the problem records a real transaction. Dimensions can be chosen to make a procedure work cleanly rather than to describe a particular plot of land.
YBC 7289 offers another example. On its face are a square, its diagonals, and numerical inscriptions, including a remarkably accurate value for the relation between a square's side and diagonal. Its reverse has been partly erased. A corresponding constant appears in other tables. The student may have been applying a known value, not deriving it on the spot.
The tablet demonstrates sophisticated handling of this numerical relation. It does not by itself demonstrate a Greek-style system of propositions and deduction. Attaching a later theorem's name can import an entire organization of knowledge along with a correct mathematical observation.
Plimpton 322 is more contested. The surviving clay is roughly thirteen centimeters wide and nine high, a few centimeters thick, with a damaged edge and a marked surface. Four columns and fifteen complete rows remain; material may be missing on the left.
George Plimpton acquired it from an antiquities dealer around 1922–23. The dealer associated it with Senkereh, ancient Larsa. Without a recorded excavation, that attribution cannot become a secure findspot. The tablet subsequently entered Columbia University's collection.
In 1945, Otto Neugebauer and Abraham Sachs identified numerical relations corresponding to the sides of right triangles. Those relations can be checked. The dispute concerns the purpose of the table.
Calling it the world's first trigonometric table gives it an immediately familiar identity. Robson's reassessment in 2001–02 challenged that identity. Old Babylonian evidence does not supply the later conceptual apparatus of angular trigonometric tables. Reciprocal pairs, school tables, problem construction, and the tablet's format have closer parallels within its own documentary setting. She read it as connected with a teacher's preparation of problems. A strong claim for exact sexagesimal trigonometry was advanced again in 2017.
The right-triangle relations are not in doubt. The historical label remains a matter of interpretation. A defensible account can explain reciprocal pairs and educational uses without pretending that the debate has a single uncontested verdict.
Something similar happens when historians translate verbal procedures into algebra. The tablets do not present symbolic equations in our notation. Akkadian instructions describe lengths, widths, adding, removing, holding together, and completing areas. Neugebauer and François Thureau-Dangin's major decipherments made the underlying mathematical relations strikingly visible in modern algebraic form.
That success carried a risk: a modern equation on the printed page could be mistaken for the object the ancient scribe had consciously manipulated. Jens Høyrup's work on the language instead emphasized operations on measured lines and areas—cutting, joining, and completing shapes. Different modern formalisms can reproduce the result. Understanding what the scribe understood requires attention to the words.
Return to the graded problems. They do not end in a settlement. The same scribal world was making two sorts of record: one would go to a storehouse or an office; another would go into the hands of a learner.
They shared material, vocabulary, and notation. Their destinations differed. One followed deliveries and harvests. The other could follow a sequence of difficulties. Once that second rhythm existed, it did not need a new administrative order to justify every next question. A bad harvest did not make it pointless for the next exercise to be harder than the last.
There is no reliable percentage for how much of the corpus was purely practical or purely intellectual. A reciprocal table could be both schoolwork and preparation for future accounting. A fictitious field problem could train a real professional skill. Counts of known mathematical cuneiform texts—often put at roughly two thousand, with a substantial share still awaiting full publication—do not sort their purposes for us.
An apparatus developed for keeping track of things had begun producing work that was not itself keeping track of any consignment at all.
In the same buildings. With the same hands.
7. On the other river
The imbalance in surviving evidence is striking. Surveys often count only about twenty-five specialized Egyptian mathematical documents, containing around a hundred problems, most concentrated in two papyri. Compare that with roughly two thousand mathematical cuneiform texts.
Preservation is an unavoidable part of the comparison. Clay can survive drying and sometimes benefit from fire. Papyrus, leather, and wood decay in damp deposits. Much of the Nile Valley and Delta—the very places where agricultural administration flourished—offered poor conditions for their survival. Twenty-five against two thousand is not a fair league table of mathematical activity. Among other things, it compares soils.
The best-known Egyptian document is the Rhind Mathematical Papyrus. Its two major sections in the British Museum are about 296 and 198.5 centimeters long, both roughly thirty-two centimeters high. Fragments are also held in Brooklyn. Even the two large sections together approach five meters; the original roll was longer. Imagine not a book to leaf through but a narrow sheet extending beyond the width of an ordinary living-room wall.
At its beginning, the scribe Ahmose gives his name and dates the copying to year 33 of King Apepi. He also says he worked from an older text associated with the reign of Nimaatre, generally identified as Amenemhat III.
That earlier copy no longer exists. Ahmose's statement, made roughly three centuries later, is our evidence for it. We cannot check whether he copied every line, selected material, updated numbers, or combined sources. The tradition he reports is valuable. It is not an invitation to invent the missing manuscript.
Copying was not necessarily a secondary act. It kept something in existence. It also gave the copyist an opportunity to determine what would travel onward. Ahmose left a name and a date, more than most people who held a pen in his world.
One Egyptian text explains why a child might be encouraged to join that profession. A father takes his son on a journey and disparages occupation after occupation. Carpenters exhaust themselves. Brickworkers are covered in dirt. Laundry workers labor near crocodiles. Fishermen, arrow-makers, messengers: each trade is made to look miserable. The conclusion returns insistently. Be a scribe.
The composition belongs to a Middle Kingdom tradition, but the complete copies and many school manuscripts that survive are later. Generations of pupils copied an argument for becoming the sort of person who could copy it. Whether read as satire or professional self-promotion, it is not an occupational income survey.
A later school document, Papyrus Lansing, makes the farmer's position particularly bleak. A scribe arrives to assess the crop, accompanied by armed attendants. Grain is demanded; the farmer has none. Beating and restraint follow, extending to his family. The repeated advice is, again, to become a scribe.
This is an instructional text, not the record of a particular collection visit. Yet the person arriving to demand grain belongs to the profession the text recommends. That reversal should not disappear when we admire literacy.
Returning to the Rhind mathematical roll, its modern history also contains gaps. Rhind bought the principal material at Luxor in 1858, reportedly from the area near the Ramesseum, without a documented excavation. The British Museum acquired the main sections in the mid-1860s. Edwin Smith bought further fragments, later recognized as joining the roll; his daughter donated his collection in 1906.
The other mathematical objects have their own unusual shapes and histories. The Moscow Mathematical Papyrus is roughly five meters long but only four to eight centimeters high: more a strip than a broad sheet. Its twenty-five problems include the volume of a truncated pyramid. Vladimir Golenishchev acquired it on the antiquities market in 1893, again without a secure archaeological findspot.
The Egyptian Mathematical Leather Roll, about twenty-five by forty-three centimeters, preserves repeated decompositions into unit fractions. It entered the British Museum with Rhind's material but remained rolled up for decades. Dry leather had become so brittle that opening it risked destroying it. Treatment finally allowed it to be unrolled in 1927.
By contrast, the mathematical material from Lahun belongs to excavations of a Middle Kingdom settlement. It can be placed within an archaeological context rather than only a dealer's account. Mathematics forms a small part of the papyri recovered there.
Egyptian methods ordinarily expressed a fractional quantity as a sum of distinct unit fractions, with some special conventions. The Rhind roll opens with a table decomposing a class of fractions into workable components. It supports division, doubling, rationing, and the distribution of quantities that cannot be handled merely by repeated halving. Problems about bread, beer, grain, and labor draw upon the same repertoire.
A smaller related table from Lahun helps establish that the Rhind table belongs to a tradition rather than appearing from nowhere.
These methods fitted certain operations naturally. Other calculations required longer expressions and trained choices among decompositions. Calling the system clumsy measures it against our notation. Corrections and auxiliary tables demonstrate a demand for skill; they do not tell us that the scribes themselves experienced their system as inefficient.
Egyptian school mathematics also produced problems that no real account was likely to require. Rhind problem 79 presents a cascade of sevens: houses, cats, mice, ears of grain, measures of grain. Each level multiplies the next. The question concerns their total.
No granary official needed to find exactly seven cats in each of seven houses. The familiar nouns carry an exercise in powers and summation. It has the extravagant pleasure of a riddle. Someone turned an escalating numerical pattern into work for a student.
Other problems, notably 56–60, concern the seked: a way of expressing a slope through horizontal displacement in palms and finger-widths for a vertical rise of one cubit. We can describe the relation with later mathematical language, but the text does not use our angles or trigonometric functions.
For Old Kingdom construction, Merer's logbook from Wadi el-Jarf supplies a different kind of first-hand evidence. It belongs late in Khufu's reign, to the year after the thirteenth cattle count, conventionally converted to approximately regnal year 26 or 27. Merer supervised a group of roughly forty boatmen within a larger crew. The log records journeys carrying limestone from Tura to the works at Giza.
Merer was an inspector, not a mathematician in the later professional sense. He had people and stone to deliver on a schedule. His records show the coordination that an enormous building project required. Quarry traces, crew marks, and workers' settlements provide further evidence of organized construction.
What does not survive is a Khufu-period worksheet proving that its designers followed a particular procedure from the Rhind roll, copied nearly a millennium later. We can reconstruct a pyramid's slope in seked units and notice convenient ratios. Inferring some equivalent method of slope control is reasonable. Identifying the exact written procedure remains an inference.
Capacity measures offer another example. The hekat could be divided repeatedly, and surviving problems use those fractional units. Later writers connected that sequence with a beautiful myth about a damaged eye. The beauty deserves a closer look.
For now, Ahmose's name remains at the head of the roll. He identifies himself through the act of copying. The modern label mathematician comes from our side of the encounter.
8. The words that went missing
The most familiar story about geometry's beginnings comes from Herodotus.
An Egyptian king, he says, divided land into equal plots and collected an annual rent. When the Nile took part of a plot away, surveyors measured the loss and the rent was adjusted. Herodotus then offered his own conclusion: he thought geometry had originated in this way and later reached Greece.
There are two distances to keep in view.
One is chronological. Herodotus wrote in the fifth century BCE. If the royal traditions behind his story chiefly reflect the Middle Kingdom, they concern a world roughly thirteen to fifteen centuries earlier. Even a looser reading leaves him much later than the mathematical tradition represented by the Rhind roll.
The other distance is inside the sentence. He marks the origin claim as his inference. Remove that qualification and a traveler's explanation becomes an ancient archival fact.
The unqualified version is easier to remember. It travels further.
There is abundant evidence that Egyptians surveyed land: area problems, land records, measuring practices, and taxation documents. What we do not possess is an Egyptian document announcing that geometry was invented because floods erased the boundaries.
The story acquired accessories. A rope divided by twelve knots, a three-four-five triangle, the recovery of a right angle: these details are not in Herodotus's account. Their familiar use in stories about Egyptian geometry belongs to much more recent histories.
As the picture becomes more detailed, the details can become younger.
The fractions of the Eye of Horus offer a further example. In the attractive modern account, Seth tears the eye apart. Each recovered piece corresponds to a successive fraction: one-half, one-quarter, one-eighth, down to one-sixty-fourth. The pieces nearly complete the eye; Thoth supplies what is missing. Myth, mathematics, damage, and restoration seem to fit perfectly.
Jim Ritter traced the modern construction of that correspondence. The relevant capacity-fraction signs in early Middle Kingdom material are hieratic signs. No surviving ancient text identifies the six marks as six parts of the eye. Strong visual correspondences were developed in modern Egyptology and became familiar through sign lists and histories of mathematics, especially in the early twentieth century.
The myth of the injured and restored eye is genuinely ancient. The explicit pairing of six parts with those six fractional signs is another matter. A compelling synthesis can be thousands of years younger than the objects it seems to explain.
These stories have an additional advantage over a sober account of the archive: they do not need an identifiable person. There are too few surviving names to give an inventor a biography, so the invention is attributed to Egypt, or to a river.
The nilometer invites a comparable shortcut. Egyptians recorded inundation levels from early periods. Columns, stairs, and wells could serve as measuring installations, with cubits marked on them. Too little water threatened irrigation; too much could damage crops. It is reasonable to connect knowledge of water levels with estimates of agricultural resources and the state's capacity to collect revenue.
But that broad connection is not a surviving Pharaonic tax table that automatically converts so many cubits of water into a particular tax rate. Detailed evidence connecting water measurement and taxation is richer for Ptolemaic, Roman, and especially Islamic periods. The famous nilometer at Roda dates to 861 CE. It cannot be borrowed unchanged for a much earlier world.
Returning from origin stories to surviving records brings their unevenness into focus. Estimates of known cuneiform objects range from several hundred thousand toward a million; by 2016, more than 300,000 had been catalogued. Only a small part is mathematical. Ur III administrative documents alone vastly outnumber the specialized mathematical corpus, while Egyptian mathematical texts survive in only a few dozen objects. The exact totals depend on the date and the counting rules. The asymmetries are unmistakable.
They produce several kinds of blindness.
The cheapest and most frequent exercises were often the easiest to erase. The Nile floodplain is much less audible than dry settlements and desert burials. Sophisticated written work is more visible than an ordinary person's mental arithmetic, knotted records, estimate by container, or spoken account of a debt. Repetition and memorization mattered in schools, but no calculation gives us the exact share of teaching that happened orally.
There is also the question of who held the stylus. It is not correct that all scribes were men. Evidence for female scribes reaches back into the Akkadian and Ur III periods and becomes clearer in Old Babylonian material. Scholars have identified school texts signed by women, ranging from elementary exercises to literary work. Women in particular Old Babylonian communities also managed property and documents; Amat-Mamu is a well-known example.
At the same time, many women and enslaved or dependent people appear in the accounts as people being counted. Textile workers, children, and laborers become rations and workdays under someone else's administrative responsibility.
Both observations belong in the picture. One cannot cancel the other.
An archive is produced by people with access to recording. Its silence about everyone else is a feature of that production, not a census of intellectual ability. The absence of mathematical tablets signed by ordinary farm workers cannot prove that farm workers were unable to calculate.
Who first taught children outside scribal households to count? How much arithmetic remained entirely unwritten? What complete design procedures did early builders use? How did oral accounting work before writing at Uruk? We do not know enough to reconstruct these worlds in full.
The surviving tablets are the ones someone kept, or the ones a fire happened to harden. The exercises smoothed away for tomorrow's lesson have nothing more to tell us.
The child rubbing the clay flat did not know that he was removing evidence.
The reckoning continues. What counts as mathematics is still not finally settled.
一 数羊和数谷子用的不是同一套符号
一群羊要分给三个人。
这件事未必需要写下数字。把羊赶成三堆,看哪堆矮了就从别堆牵一只过去,来回几次也就分完了。事后谁也说不清自己究竟牵走了几只,但那天下午三个人都没有意见。
难的是另一些情况。羊今年要交上去一部分,交多少取决于去年欠了多少。羊分散在几个村子,而收羊的人不在场。收上来的羊还要折成粮食再发下去,折算的比例是别人定的。到这一步,赶成三堆的办法就不管用了。有人必须把它记下来,而且记下来的东西要能在另一个人手里,在另一个月份,被读成同一个意思。最早那批泥板,做的就是这件事。
先想象两份记录。下面是说明记数方式的示意场景,不是两块已有明确编号、可以逐一指认的实物。
把时间放在前3300年前后的乌鲁克。一块掌心大小的泥板,上面压着记号。它记的是一批牲畜,有多少头,写在上面。
另一份记录来自同一座城、同一个时期,记的是一批大麦的容量。今天的人容易预期,记录人只要换掉商品名称,仍可使用同一套通用的数字。但当时不能这样简单地套过去。
不是有人写错了,也不只是同一套数字换了字体。点清牲畜和量一批大麦,当时可能进入两套不同的数值系统。
这听起来像个笔误,但它是当时书写系统的基本构造。乌鲁克的书吏手里没有一套脱离对象,放到哪里都通用的数字。他有好几套。人和牲畜这类可以一个一个点清的东西,走一套系统。谷物的容量,走另一套。土地面积,又是一套。长度还是一套。某些谷物制品和口粮甚至有自己专门的进位方式,和普通的点数系统并不是同一种字体的两种写法,而是两件不同的东西。
后果是,一个符号的值取决于它正在数什么。把它从牲畜那一栏原样抄到谷物那一栏,得到的不是同一个量。要读懂一块泥板,得先知道板上那批东西属于哪一类。类别不清,数字就悬着。
这不等于书吏永远换算不了。单位之间有关系,关系可以学。真正的意思是,换算不是从数字内部长出来的,是从外部加上去的。这些记号的读法,还没有完全摆脱所计对象与单位的约束。
这带来一个很实际的后果。一块泥板一旦离开产生它的那间屋子,就可能变得读不出来。记录的人知道自己在数什么,所以不必写下来,而没有写下来的那一部分,恰恰是让数字有值的那一部分。后世研究者面对一块没有出土层位的板子时遇到的困难,有一半是当年那个书吏省下来的功夫。
也不该把这套安排读成粗糙。它是贴着实物长的。谷物的容量单位跟着实际的容器走,面积单位跟着地块的丈量方式走,每一套都在自己那一摊事情上顺手。一个牧人清点羊群和一个仓吏收谷子,本来就是两种动作,两种动作各自积累出一套记号,一点也不奇怪。
从使用的角度看,分开甚至更省事。仓吏一辈子只跟容量打交道,不需要一套能同时数羊的符号。每一套系统都砍掉了自己用不上的部分,有时反而比通用系统更顺手。麻烦只在两套东西要对起来的时候才出现,而那种时候在一个村子里并不多。
要对起来的时候在一座城里就多了。城里有仓,有神庙,有工程,有一年到头的进出,谁欠谁多少必须放在一起看。那些互不通约的记号后来被压进同一套东西,压力来自这里。奇怪的是后来它们被压进了同一套东西,而那件事要再等一千多年。
现存最早的这批泥板上,记的几乎都是谁交了多少,还欠多少,发给了谁。它们不是为了留给后人看的。它们是为了下个月还能查得清。
二 最早的书写里,五分之四以上是账
原始楔文材料今天通常谈到六千块左右的泥板与残片,其中约五千件出自乌鲁克本身,另有一部分来自杰姆代特纳斯尔等受乌鲁克书写传统影响的地点。按传统分期,这批材料横跨约前3350年至前3000年。
尼森对这批最古老文本做过一个经典统计。经济与行政记录约占百分之八十五,词汇表一类的非行政文本约占百分之十五。而且那百分之十五主要是在较晚的阶段才增长起来。在更早的层位里,词汇类文本极少,行政登记几乎是压倒性的。
所以如果问,今天实际拿到手里的最早的书写,账目占多少,答案不是过半,是绝大多数。
这些账目不是后世意义上的簿记,多半是短记录,一个数量符号,一个商品或人员符号,一个机构或个人的标记,拼在一起。当时的书写还没有发展到能自由记录完整口语的程度,数量,单位和物类反而比句法更清楚。也就是说,这套系统最擅长表达的,是多少什么给了谁。除此之外它一时还说不了太多。
人名也是跟着账进来的。乌鲁克的十八块板子上,反复出现同一对符号,读作库辛,跟大麦和酿酒用的粮食写在一起,其中一块记的是三十七个月里经手的大麦总数。库辛是一个人,一个职位,还是一个机构,不知道:这对符号前后几乎没有别的字。常见的一种解读是把它当成一个人。如果是,那么今天读得出来的最早的一个人名,是一笔大麦账上的名字。
这里必须停一下。百分之八十五说明的是幸存下来的那一批。泥板特别适合保存行政记录,尤其是被丢弃后晒干,或者被一场建筑火灾意外烧硬的那些。而大量一次性的标记,木头,纤维,口头指令,以及反复揉掉重来的练习,不会以同样的概率留下来。从成品档案的比例,倒推不出发明者当初唯一的动机。
这个区别看上去琐碎,却决定了后面所有的话怎么说。行政需求是书写成形的核心环境,这一句站得住。会计是书写唯一的原因,这一句站不住。两句之间隔着的不是证据的多少,是证据能承担的重量。
尼森,达梅罗,英格伦德的说法比较谨慎,最早文字的成形与城市机构越来越复杂的资源管理紧密相连。这句话和人类为了记账发明了文字,差着一大截。前一句是环境,后一句是动机,而动机没有留下任何一份前3400年的自述。
同一个区别也出现在筹码上。近东从新石器时代到城市化时期确有大量小型黏土几何体,圆锥,球,圆盘,还有把它们封起来的泥球和带外部压印的容器。施曼特贝瑟拉据此提出过一个长达数千年的连续谱,简单筹码对应商品数量,复杂筹码对应更复杂的物类,筹码装进泥球,再压在球面上,最后二维压痕取代三维实物,于是有了书写。
实物是真的。泥球里确实装着筹码。但这条链子后来被逐段拆过。形态相似不等于功能和语义的连续。分类分得过于整齐,很多筹码根本没有明确的会计出土语境。筹码形状与最早文字符号之间的一对一对应,也不像那个强说法要求的那样成立。至今没有足够的证据,把整个史前的这一类对象统一解释成会计装置,许多东西可能本来就是多用途的。
现在比较常见的处理是这样,部分筹码,封泥和数值压印属于会计技术的谱系,这个弱版本接受度不低。一个持续数千年,意义稳定,能够逐个导出文字的统一代币体系,不是共识。
三 人变成工日
到了乌尔第三王朝,情况完全不同了。这个王朝留下的行政文书,单是已知的就在十二万件的数量级上。
这些文书里最能说明问题的一类,是核账或者平衡账。它不是一张简单的收支表,而是把一个责任期拆开来算。先是应交或应完成的总额,然后扣掉合法支出,损耗和已完成量,相减得到差额,差额再判为结余或者亏空,最后是日期,负责人和核账说明。
关键的一步在于折算。劳动力被换成工日。粮食,羊毛,纺织,农业作业,也都能按规范生产率折成可比的量。乌玛等地的文书显示,人员通常按工头或监工来组织,而行政这一端关心的不是今天来了几个人,是这支队伍按规矩应该交出多少个劳动日。
于是账目的中心站着的不是工人,是监工。
折算这一步做完之后,有些东西就看不见了。一个人今天病着,一个人手脚比别人慢,一个人干的是最重的那一段,在工日这个单位里全都一样。账目并不否认这些差别,它只是没有给这些差别留位置。能进入总账的只有一个数,而这个数一旦进去,后面所有的加减就只认它。
舒尔吉三十七年到四十年之间有一组记录,把数百名女性劳动力以及她们的劳动和谷物责任,连续记在一个叫卢乌鲁布的人名下,此人是米纳尔尼之子。这类档案说明工头不是每天点个名的角色,而是一个长期挂账的责任节点。账户以负责人的名字连年出现,后世的学者才有可能把责任会计这套东西重建出来。
亏空可以结转。不足的部分作为欠额留到下一期,超出的部分记为盈余,下一张总账可以把上一期的余额吸收进来。一个人的名字因此可以在账面上背着一笔数字走好几年。
总账背后还压着一层东西。收据,带封印的凭证,小额单据,在核验之前一直保留着。核账做完,它们的证明价值才改变。乌尔第三王朝甚至形成了保存这些支持泥板的容器传统。所以一份平衡账不是一块泥板,是一块泥板加一筐泥板。
有一个说法流传很广,说某个工人死后,他没完成的定额会转给家属。这条得停下来。确实有文书记录死亡,人员替换,也确实有死者家属或孤儿的配给。也确实有工头账户结转亏空。但把这两种证据合起来,变成死者把劳动债传给儿子,目前找不到一块泥板同时写明某人死亡,尚欠多少工日,该欠额转予某某亲属。站得住的只有一句:这套会计可以让账户中的亏空跨年度存续。至于个体工人的未完成定额是否在他死后按继承规则转为家属债务,没有直接实证。
这一条之所以容易滑过去,是因为它太顺手了。一个能把活人折成工日的系统,顺着想下去似乎理应把债也折给儿子。推理很漂亮,材料却没有跟上。系统做得到的事和系统实际做过的事,中间隔着一层,这一层在没有证据的时候不能自己填上。
同样,监工对亏空负责这件事基本成立,但那是一个行政责任账户挂在他名下,不等于后世民法意义上的个人无限债务。卢乌鲁布名下的数字是不是真要他从私人财产里补齐,证据还不够。他是米纳尔尼之子,这一点泥板上写着。他家里有什么,泥板上一个字也没有。
不管怎么说,有一件事是清楚的。到这个时候,一个南方城邦的行政系统已经能够把几百个活人,他们一年的力气,他们吃掉的粮食,全部换算成同一种可以相加相减的东西,并且把结果挂在一个人的名字下面。
四 抽象层
第三千纪后期开始,特别是在乌尔第三王朝,可以看到另一个方向上的动作。书吏越来越多地先把具体的度量转换成抽象的六十进制位值数,在这个抽象层上运算,算完再转回实际单位。
这里要把两件事分开。以六十为重要进位节点的计数传统,在乌鲁克时代就已经存在。但真正把数字从商品单位里抽出来,让同一组符号按位置表示不同的六十次幂,是第三千纪后期才清楚出现的,乌尔第三王朝进入运算实践,到古巴比伦的学校完全成熟。支撑这个抽象层的,是表。
古巴比伦的标准倒数表并不把从一到五十九全部列一遍。它主要列那些在六十进制里有有限倒数的数,一张典型的表大约二三十行。至于那些没有有限倒数的数,表里干脆不列。需要的时候可以分解,近似,或者换别的算法。乘法表则把某个关键数与一系列乘数的结果逐行排开。度量衡表负责把传统的长度,面积,容量,重量单位,换成抽象的六十进制量。学生实际运算的核心技巧,可以概括成一句话,除法变成乘以倒数。先在背熟或查到的体系里找到除数的倒数,再乘上去。所以这些表不是附带的参考物,是计算本身赖以进行的地基。
对一个学生来说,这意味着他要背的东西和他会做的事情是同一件。背下一张倒数表,他就能做除法。背不下来,他手里那些数字就不动。技艺装在记忆里,而记忆要靠一遍一遍在泥上重来。学校留下的板子里表格占了那么大一块,原因就在这儿。
这套位值数有一个醒目的缺口。早期通常没有固定的小数点,也没有后世意义上的内部零符号。同一个书写形式,理论上可以相差六十倍,三千六百倍,或者六十分之一。书吏靠问题里的单位,数量级和语境,把绝对值恢复出来。也就是说,尺度不写在数字内部。
目前也没有找到一块泥板,能证明某个书吏因为没有零而明确算错,且排除得掉抄写错位一类原因。缺口存在,但它似乎并没有把人绊倒。
换个说法,这套记法把一部分工作留在了板面之外。数字负责相对关系,人负责记住这批数说的是谷子还是银子,是一整仓还是一天的口粮。它不是一套自足的系统,是一套需要有人在旁边看着的系统。
统一发生在哪一层,这一点要紧。没有哪个国王一夜之间废掉所有单位。容量,重量,长度,面积仍旧各有各的单位,商人和仓吏照旧用它们。被统一的是计算的那一层,各种单位都能通过标准换算表映射到同一个抽象体系里去。度量衡表就是这两层之间的那道门。
现代文献有时把这一轮标准化简称为舒尔吉改革。这个标签方便,但没有一块可以相当于近代度量衡法的舒尔吉诏版,逐条宣布从今日起某个单位等于多少。能说的是,舒尔吉漫长统治下的这个国家显著推进了度量,税役与账目的标准化。具体哪些单位关系由国王亲自下令确立,是由后来一致的文书制度倒推出来的。
关于舒尔吉本人,倒是有一段极好用的材料,而且必须降级使用。舒尔吉赞歌里,他自称少年时进过学校,学过苏美尔和阿卡德泥板的书吏技艺,能熟练处理减法,加法,计算和会计。另一篇赞歌称他是有知识的书吏。问题在于,现存的赞歌抄本主要是古巴比伦时期的学校抄本,大约在舒尔吉生活的年代之后二三百年才写下来。它们可能保存了宫廷赞歌的传统,但不能证明历史上的舒尔吉少年时真的坐过那样的课堂。今天通常把它当作王权意识形态和理想博学君王形象的证据,而不是一份履历表。
一个国王愿意让人把会记账写进自己的颂诗,这件事本身已经说明了不少。
五 一栋房子里的一千四百块泥板
尼普尔有一处民居,发掘者按字母顺序给同一片街区的房子编了号,它排在靠后的位置。这栋房子里发掘出的泥板与残片约一千四百二十五件,其中百分之九十以上是书写练习。这一点让它和大量来路不明的数学泥板完全不同,这里可以把教材放回一栋真实房屋的房间和废弃层里。
练习板的形式本身就很有画面。有一类板子,正面一栏保存教师写下的范本,旁边是学生的复制区,背面可能抄一些较长,较早学过的材料。另有一种小圆板,教师先写一行,学生在旁边重复。学生的练习区经常被抹平,重新利用。
一块板可以用很多次。这件事在当时是省钱,在今天是损失。学生练过什么,错在哪里,改了几遍,大部分随着那一层被抹掉的泥一起没了。留下来的是他最后没来得及抹掉的那一次,或者是他终于写对之后搁在一边的那一块。
泥板的手感差别很大。耶鲁那块编号七二八九的圆板直径约八厘米,一只手掌就能托住。大英博物馆编号一三九〇一的那块约十九点四厘米宽,十一点七厘米高,已经需要两只手或者一张桌子。写错了怎么办,趁湿用手指或工具抹平,重写。泥板一旦彻底干透,就没有那么容易改了,所以正式的板子上常常能看到重刻,挤字,局部擦抹留下的不平整。
课程的顺序是重建出来的。廷尼,罗布森,韦尔德惠斯等人根据板型,文本组合和抄写方向,拼出了尼普尔的基础序列。先学怎么做楔,怎么写单个符号,随后是一类符号练习,接着抄音节序列,再进入人名列表和按类别排列的词汇表,然后是更复杂的词汇系列,计量表,数字与表格。基础训练完成之后,学生开始抄王赞歌,格言,争辩文学和神话。
这个从第一天到最后一天的说法要留一个注脚。手上有的是考古学重建的序列,不是一张古代的课程表。学生可能重复,可能跳过,可能并行练习。一栋房子的材料也不该无条件推广成整个巴比伦的教育制度。罗布森本人对这种推广就很警惕。
古巴比伦文学里有一类后来被称作学校生活的对话文本,而且它们就是学生要抄的材料。其中一篇从早晨写起。学生拿着泥板去学校,朗读自己那一块,吃午饭,准备新板,回家之后还要在父亲面前把当天的东西复诵一遍。
第二天上午,教师检查他的板子,发现有地方缺了。棍杖第一次落下来。
接下来的事情才是这篇文本真正的样子。管功课的人打他,说了什么,泥板上残了。管院子的人打他,问他为什么趁自己不在就说话。又有人打他,问他为什么不把头抬好。管画图的人打他,问他为什么从座位上站起来。管门的人打他,问他为什么走出了门。又有人打他,问他为什么拿了一样东西,那样东西的名字残了。管苏美尔语的人打他,因为他在该说苏美尔语的时候张口说了阿卡德语。最后是他自己的老师,说他的字写得不好。连早上那一次算在一起,一天之内九次,理由一条比一条更细。
当天晚上,这个孩子的父亲把那位教师请到家里,端上酒和食物,又送了衣物。教师喝完酒,转过头来称赞这个学生。
这一幕好用得几乎让人不想去核。所以要马上说清楚,它来自学校文学,不是当天的纪律记录。这类文本产生于古巴比伦时期,不像后面要谈的那位希腊人那样晚了一千年,但体裁仍然是文学。连续挨打和请客宴饮可能利用了真实的制度,不能证明每所学校每天如此。
泥板形态能够独立支持的是另一部分。教师范本和学生抄本确实并排存在,学生区确实有重复,磨掉和重写,高级学生确实抄文学。教师示范,学生模仿,检查纠错,这条线很稳。
乌尔另有一处房子,门牌被现代发掘者记作安静街七号,出土两千余件文书和练习材料,属于库宁伽尔一家。常见的标签说这是一个世袭书吏家族,这个标签得改。库宁伽尔和他的几个儿子有净礼祭司的身份,家中进行教学是可靠的,说他们整个家族的主业就是书记员则过度简化。可考的人物包括他的儿子乌尔南纳,印章上称他为与月神相关的祭职人员和档案负责人。
至于是不是世袭,最好的回答是有强烈的家族连续性,但没有法律意义上的封闭资格。识字技术,泥板收藏,人脉和官职资源集中在家庭里,自然形成优势,而姓名和职衔的变化又说明并不存在一个固定的书记种姓。报酬也没有统一的工资表,粮食,羊毛,土地收益,口粮以及职务本身都可能构成收入。从书吏受尊重推不出每个低级抄写员都富裕。
学校面向平民天才开放,识字因此成为社会上升阶梯,这个说法的直接证据很弱。现有的学生档案明显偏向那些已经握有行政和祭司资源的家庭。一个普通农业家庭的孩子进入高级书吏训练的概率是多少,算不出来。
六 没有出口的题
大英博物馆那块编号一三九〇一的泥板,四栏,二十四道关于正方形和矩形边长与面积的题目,从简单向复杂排列。它不是科学发掘出来的,没有安全的出土层位。
把这二十四道题读一遍,有几件事很难忽略。它们排成了一个梯度。同一个操作被反复变形。数字被挑得异常整齐。
排成梯度这件事需要有人来做。第二题比第一题难一点,第三题又难一点,这个顺序不会从任何一笔账里自然长出来。它要求有人先想清楚哪一步是关口,再造出一批只在那个关口上有差别的题。造题的人心里装的不再是某一块地或者某一仓谷子,是学生会在哪里卡住。
这类题目往往穿着行政的外衣。田地,砖块,沟渠,劳工,银子,粮食,这些是书吏职业世界里的标准对象,出现在题面上再自然不过。但没有哪个粮仓管理员会在工作中遇到这样一道题。给定的尺寸是为了让程序跑得顺,不是为了让某块地被丈量。
耶鲁那块圆板也是同一类东西。直径八厘米,一只手就能拿,出处不明。正面画着一个正方形和两条对角线,一条边上写着一个数,对角线附近写着两个数,其中一个是正方形对角线与边之比的极精确值。背面有一部分被抹掉过。常数表里保存着同一个对角线常数,所以这个学生很可能是在使用一个已知的常数,不一定是当场把它算出来的。
这块板证明的是古巴比伦人能够以很高的精度处理正方形对角线的关系。它不证明他们拥有希腊式的命题与演绎体系。用后世的定理名字去称呼它,是把一整套知识组织方式偷偷塞了进去。
争议最大的是那块普林顿三二二。它宽约十三厘米,高约九厘米,厚两到三厘米,沙黄色,表面有铁锈橙和黑色的斑驳,还有明显的刮痕,边缘残损。现存四栏,十五个完整数据行,左侧原来可能还有缺失的部分。
它的来路可以一步一步排出来。乔治普林顿大约在1922年至1923年间从一个古物商手里买下它。卖方说来自森克雷赫,也就是古代的拉尔萨,但没有科学发掘记录,所以这个出土地不能升格为确定的层位。二十世纪三十年代,它随普林顿的藏品进入哥伦比亚大学。
1945年,诺伊格鲍尔与萨克斯认出表上的数值与直角三角形的边长关系相合。这个数学结构可以检验,从来没有争议。有争议的是它是什么。
后来有作者把它称为三角函数表,甚至称为世界上最早的三角函数表。罗布森在2001年到2002年的重新分析反对这种读法,理由是古巴比伦文献里没有与后世角度函数表相当的概念体系,而倒数对,学校乘法表,问题生成和表格格式,都有大量本土的平行证据。她据此把它解释成教师用来准备直角三角形题目的一张工作表。2017年又有人重新提出精确六十进制三角学表的强说。
比较稳妥的裁定仍然是,泥板与直角三角形关系,倒数对以及学校问题生成密切相关。把它叫作三角函数表,需要引入古巴比伦材料自身没有提供的概念。
这类命名问题不止一处。原始的泥板上没有符号方程。它们用阿卡德语的动词描述操作,长度,宽度,使其相持,撕去,附加,组成正方。二十世纪三十年代到四十年代,诺伊格鲍尔与蒂罗多丹第一次大规模破译这批文本,并用现代代数把程序压缩成方程。这一步在揭示数学结构上极其成功,却带来一个副作用,读者容易把方程当成古代书吏脑子里实际存在的对象。许律普后来从语言出发重读,认为那些看似解二次方程的操作,本土语义往往指向可测线段和面积的拼接,切割与补形。今天通常承认两种现代语言都能把结果形式化,但要问书吏自己在做什么,语文学的重建更贴着词汇证据。
回到那二十四道题。它们不是账目,不会进入任何一笔结算。同一批房子里,同一批手里,产出的东西已经分成了两种。一种最后要交上去,另一种交给谁都没有用。
这两种东西共用一套词汇,共用一套记号,甚至共用同一批泥。区别只在出口。前一种走进仓库和王室,后一种走进另一个孩子的手里。而后一种一旦开始生产,就有了自己的节奏,它按难易排序,不按收成排序。这个节奏一旦立住,就不再需要外面有人下令。今年的收成好不好,不影响第二题该不该比第一题难。
不能给出一个百分比。用途不是目录上可以直接清点的物理属性,一张倒数表既是学校练习也可能服务于未来的会计,一道田地题可以完全虚构而训练的是真实的职业技能。可以可靠引用的是数量级,已知的数学楔文文本约两千件,其中约一千件已有转写和翻译出版,另有大致相同数量还在等待整理。这两千件里,乘法表,倒数表,平方与平方根表,计量表和学校题目占了很大一块。
整套记账的手艺是为了清点而立起来的。等它站稳,它已经开始生产一些不清点任何东西的东西,就在同一批房子里,出自同一批手。
七 尼罗河那边
埃及的情况先要说一个数量上的落差。整个法老时期及其后,能够算作专门数学文本的材料大约二十五件,现存问题约一百道,其中绝大多数集中在两卷纸草上。相比之下,楔文数学文本已知约两千件。
理解这个落差,保存条件是不能绕开的原因。黏土即使只是晾干也能长期存在,一场建筑火灾还可能把它烧得更硬。纸草,皮革和木板一旦进入潮湿的土层就极易腐烂,而尼罗河谷和三角洲的农业官署,恰恰处在最不利于有机物保存的位置。把二十五和两千放在一起比较两地的数学活动,比较的其实是土壤。
最重要的那一卷叫莱因德数学纸草。它现在分成几段,大英博物馆的第一段长约二百九十六厘米,高约三十二厘米,第二段长约一百九十八点五厘米,同样高约三十二厘米,另有若干碎片在布鲁克林。两大段加起来已近四点九五米,加上碎片和失落的接缝,原卷展开超过五米。它不是一本可以翻页的册子,是一条比普通客厅墙面还长的窄长卷轴。
卷首署着抄写者的名字,阿赫摩斯。他在开头宣称此卷提供一种准确计算,用以探究事物,认识各种奥秘的知识。随后明确记年,说抄写于上下埃及王阿佩皮三十三年。又说自己依据一份古老的抄本,那个旧本制于尼玛特雷时代,也就是通常认定的阿蒙涅姆赫特三世。
旧本已经不存在了。关于它的直接证据,只有阿赫摩斯本人在大约三百年后的这一句说明。他是逐字复制,节选,更新了数据,还是拼合了多种材料,无从检查。今天通常接受他自述所保存的传统年代,但也只到这一步。
抄写在当时不是次一等的工作。一份东西能被抄,说明有人认为它值得再存在一次,而抄的人有机会决定哪些留下,哪些不留。阿赫摩斯留下了一个名字和一个年份,这已经比同时代绝大多数握笔的人多。埃及人自己怎么劝孩子去做这一行,有一篇文字说得很清楚。
它的框架是一位父亲带着儿子上路,一路上把别的行当挨个数落过去。木匠累得直不起腰。泥瓦匠身上糊满了泥。洗衣工整天泡在水里,邻着鳄鱼。渔夫,箭匠,信使,一个也没放过,每一种都被写得又脏又苦又没有指望。数落完一轮,父亲把结论重复一遍,没有哪一行比得上书吏。
这不是一份职业收入调查。它形成于中王国的传统,但现存的完整抄本和大量学校抄件主要来自新王国,也就是说,后来的孩子一代一代抄写的是一篇劝人当书吏的文章。今天有人把它读作讽刺,有人更愿意称它为书吏行业的宣传。两种读法都不把它对其他行当的描写当成实录。
不过有一点它没说谎。写这篇东西的人和抄这篇东西的孩子,是同一群掌握记号与数字的人。
新王国晚期还有一卷学校用的抄本,今天叫兰辛纸草,藏在大英博物馆,劝法一样,数落到农夫那一段写得最细。书吏在河岸下船,来查收成,身后跟着拿棍杖的随从和拿棒子的努比亚人。有人对农夫说,交粮。农夫说,没有。于是他挨了一顿狠打,被捆起来扔进井里,妻子被绑,孩子戴上了脚镣。整卷翻来覆去落在同一句劝告上:去当书吏。这仍然是劝学的课文,不是一份催粮的记录。课文里下船查收成的,正是它劝孩子去当的那种人。
再回到莱因德数学纸草,它的出土来历同样不清楚。莱因德在1858年于卢克索购得主要部分,卖方说来自拉美西姆附近,没有经过记录的科学发掘。他死后,大英博物馆在1865年前后获得主要卷。史密斯在十九世纪六十年代又在卢克索买到一些碎片,后来发现能与莱因德卷拼接,他的女儿在1906年把它们捐了出去。其余的埃及数学材料,来路和形状各有各的怪。
莫斯科那一卷长约五米,高却只有四到八厘米。它不是一张纸,是一根带子,上面挤着二十五道题,从粮仓算到面积,还有一道算截去顶部的方锥的体积。戈列尼谢夫在1893年从古物市场买下它,同样没有出土地点。
还有一件东西不是纸草。那是一卷皮革,约二十五厘米乘四十三厘米,上面写着好几组等值的单位分数分解。它跟着莱因德那批材料进了博物馆,然后就一直卷着。皮革干透之后又硬又脆,强行展开等于毁掉,没有人敢动。它躺了将近七十年,直到1927年才被处理开来。
与前面几件购自古物市场的材料不同,拉罕的那一批来自有记录的发掘。皮特里在一座中王国城市里挖到它们,因此这一批有明确的考古语境,知道是从哪座房子,哪一层里出来的。数学只是那批纸草中很小的一组。
埃及书吏处理非整数的方式很有特点。一个不足整数的量,通常被写成若干个不同的单位分数之和。莱因德卷开头有一张大表,专门把一类分数拆成可以操作的组合,覆盖到相当大的分母。它的用途不是欣赏分数的性质,是帮书吏在倍增,配给和除法里处理那些没法靠简单对折得到的份额。卷子后面关于粮食,面包,啤酒和劳工分配的题目,不断调用同一套习惯。
拉罕那一批里就有一份同类型的较小的表。它比莱因德卷更早或同期,出土层位清楚,因此莱因德卷上那张大表不是孤立的发明,是一个传统。
这套体系让倍增,二等分和把份额写成标准可识别的部件变得很自然,也容易和容量单位配合。代价是某些量会变成多项之和,而选择哪一种分解需要训练和查表。称它笨拙则是拿后来的记法去量它。没有哪个埃及书吏留下过抱怨这套体系麻烦的文字。现存的错误,修正和辅助表能证明操作需要技巧,不能证明操作者本人觉得它低效。
埃及也有不通向任何账目的题。最醒目的是莱因德第七十九题。
七座房子。每座房子里七只猫。每只猫盯着七只老鼠。每只老鼠啃着七穗谷物。每穗谷物又能收出七份量器的粮。数量就这样一层一层翻上去,越翻越荒唐,最后要问的是全部加起来一共多少。
粮仓管理员一辈子也撞不上七座房子里正好各有七只猫。这道题的房子,猫和老鼠不是为了记录什么,是为了让一个学生把七的幂一层层算下去而摆在那里的。三千五百年前有人坐下来编了一个笑话,并且把它写成了作业。和两河那边一样,埃及的题目里也有大量数据被刻意挑得非常适合程序运算,题目使用粮仓,与题目是一次真实的粮仓记录,完全是两回事。
莱因德第五十六至六十题讨论一个叫塞克德的东西,用每上升一肘对应多少水平方向的手掌宽和手指宽来描述斜面。换成后世的语言这是坡度,但原文不用角度,也没有三角函数。
古王国的建筑工程另有极强的第一手证据。瓦迪贾尔夫出土的梅雷尔日志属于胡夫晚期,原文纪年为第十三次牲畜清点的次年,通常折算为在位第二十六或二十七年。梅雷尔手下是一组四十来人的船工,这样的组一共四个,合成一支工队。日志记着他们从图拉运石灰石,走水路送往吉萨胡夫的工程区,日期,人力,调配都在上面。
梅雷尔本人不是数学家,也不是后世意义上的工程师。他是一个监督员,手下四十来人,要按日子把石头运到地方。日志之所以重要,是因为它显示这样一件工程需要多少种记录才转得动,而每一项记录背后都要有人会算。会算的人不一定写过一道题,写题的人也不一定押过一趟船。采石场痕迹,工队标记和工人聚落也都在,工程的组织程度没有疑问。
但没有一张胡夫时代的坡度计算表留下来,而莱因德卷比胡夫晚了将近一千年。金字塔的实际坡面确实可以用后来的塞克德单位倒算,某些坡度还落在很整齐的掌与指的关系上,说古王国的建筑师掌握某种等价的坡度控制技术,非常合理。但从实测值反推他们就是照莱因德第五十六题那个程序设计的,仍然是推断。研究古埃及建筑图的学者提醒过,许多幸存的草图并不是后世意义上的比例施工图。
埃及的容量计量另有一套单位,一个叫赫卡特的量再一路对折下去,在粮食,配给和容量换算里真实存在,莱因德卷里有题目专门演示这些单位怎么互换。这套对折分数后来会引出一个极漂亮的说法,那个说法留到后面处理。
阿赫摩斯的名字留在卷首。他没有说自己是数学家。那个词还要等很久才被造出来。他说自己是抄写的人。
八 我认为
关于几何学的起源,流传最广的一个故事来自希罗多德。
在他的记述里,埃及的一位王把土地分成相等的方块,按年征租。如果尼罗河冲走了某人的一部分土地,国王就派人去测量剩下的面积,相应降低租额。然后希罗多德加了一句,大意是,我认为几何学就是这样被发现的,后来传到了希腊。这个故事有两处需要处理。
第一处是时间。希罗多德写作于大约前五世纪中叶。如果他笔下那位王背后主要投射的是中王国的传统,那么他距所述的王权时代约一千三百到一千五百年。即使把故事理解成一般的古埃及制度,他也比莱因德卷所属的那个传统晚了一千年以上。
第二处更要紧。他自己标了。我认为这三个字就在原文里。希罗多德把因此发明几何写成了自己的解释,不是埃及档案里的原句。后来的传抄者做的事情,是把那三个字去掉。
三个字的差别在这里很大。带着它,这是一位旅行者对自己所见所闻的推论。去掉它,这就成了一条关于起源的记载。后一种形态更好记,也更好用,于是它走得更远。
埃及人测地这件事本身没有争议。面积问题,地块记录,拉绳的测量活动,税租文书,全都存在。缺的是任何一份埃及本土的文件写道,洪水抹去了地界,因此我等发明了几何。
故事后来还长胖了。打了十二个结的绳子,用三四五的边长关系重新定出直角,这些细节连希罗多德那里都没有。它们是近现代数学史里长出来的。
把两件事排在一起看,会发现一个次序。希罗多德那句推论写于前五世纪。十二个结的绳子是近现代长出来的。越往细处看,故事的年纪越轻。还有第三个,比前两个都年轻。前面提到埃及的容量单位一路对折下去。有一个说法把这些分数讲得极漂亮。
荷鲁斯与塞特争斗,一只眼睛被撕碎。碎片散开,每一块对应一个对折下去的分数,二分之一,四分之一,八分之一,一直到六十四分之一。把碎片全部拼回去,差一点点才是完整的一只眼。差的那一份,由智慧之神托特补上。这个故事好到几乎不必核对。分数,神话,缺口,补足,一样不缺,而且缺的正好是最小的那一份。
里特追查过它的现代生成史。中王国早期的容量分数符号主要是僧侣体的书写符号,没有哪份古代文本说它们是眼睛的部件。真正把这些符号画成眼睛各部分的强版本,是二十世纪初的符号比较里逐渐形成的,二十世纪二十年代经由加德纳和数学史教材传播而成为经典。
荷鲁斯之眼被损伤又被修复的神话当然古老。六个碎片对应六个对折分数这件事,最早的明确陈述来自现代埃及学,距那个时代约三千五百年。三个故事,一个比一个年轻,而讲的都是三四千年前。
这个故事还有一个特点,不容易注意到。它没有主角。它讲的是埃及,不是某个埃及人。这一段时间留下的名字太少,少到一个关于起源的说法找不到人可以挂,只好挂在一整条河上。
同一类问题也出现在尼罗尺上。埃及很早就记录泛滥的高度,古王国的王室年代记录传统里就有年度水位数据。后世实际的尼罗尺有柱式,阶梯式,井式多种构造,刻度用肘。水位与农业潜力当然高度相关,太低意味着可灌溉的土地不足,太高又会造成破坏。国家知道水情,据此估计收成并调整征收能力,是很合理的重建。
但在这个时段里,没有保存下来一份可以写成水位多少肘等于税率多少的法老时代税则。把尼罗尺读数与税制紧密连接的详细证据,在托勒密,罗马尤其伊斯兰时代要丰富得多。今天著名的罗达尼罗尺,本身是公元861年的建筑。宏观上的关联可信,精确的机械换算不属于这个时段。把视线从故事挪回记录本身,会看到另一件事。
已发现的楔文书写物通常估在五十万到一百万之间,到2016年时已有三十万余件被编目。其中数学类约两千件。乌尔第三王朝的行政文书单独就约十二万件。而埃及的专门数学文本约二十五件。这个分布至少带来四种系统性的偏差。
最廉价,最频繁的那部分学习过程,恰恰最不容易保存。日常的湿泥练习被抹掉了,只有被丢弃后晒干或者意外烧硬的板子进入了考古记录。埃及的洪泛区几乎完全沉默,而沙漠墓地和荒漠边缘的聚落更容易留下东西,于是现代看到的样本偏向宗教,墓葬和少数干燥地点。高级文本比日常常识可见得多,一个农民,商贩或者工头怎么心算,怎么打结,怎么用容器目测,怎么口头记债,通常不会留下他自己的记录。学校本身大量依赖记忆和口授,教师范本,学生抄写,文学文本里的朗诵,反复磨掉的练习区,都间接说明口头教学存在,但课程里有多大比例是口传,算不出来。
还有一层偏差与谁握笔有关。书吏世界全是男性这个说法并不成立。女性书吏的称号至少在阿卡德和乌尔第三王朝时代已有证据,到古巴比伦更加明确,研究者已经识别出若干件由女性在题记中署名的学校文本,从基础的音节和词汇练习一直到苏美尔文学都有。古巴比伦的一个女性群体中有识字,管理财产和书写文书的实例,阿玛特马姆就是常被引用的一位。
与此同时,在乌尔第三王朝的大量账目里,女性和奴隶是被计算的人。纺织女工,依附劳动者,儿童,被换算成口粮和工日,挂在监工的名下。两件事同时为真。
档案是由握笔的人生产的。所以记录对其余人的沉默,是生产档案的制度留下的偏差,不是一次人口能力调查。因为账目里很少见普通妇女和奴隶写数学板,就说他们不会计算,这个推论方向是反的。
至于最初教人计数的是谁,非书吏家庭的孩子怎么学会日常算术,有多少算法从来没有被写下来,早期埃及建筑师完整的设计程序是什么,乌鲁克书写出现之前的口头会计是怎么运作的,这些都不知道。任何用幸存的一两卷纸草去填满这些空白的叙述,都是推测。
留下来的泥板,是有人觉得值得留的那些,或者是一场火恰好烤硬的那些。为了下一课而被抹掉的那些,什么也没有留下。那个把练习栏抹平重来的孩子,不知道自己正在清除证据。
数还在往下算,而什么算数学,还没有算清楚过。
一 數羊和數穀子用的不是同一套符號
一群羊要分給三個人。
這件事未必需要寫下數字。把羊趕成三堆,看哪堆矮了就從別堆牽一隻過去,來回幾次也就分完了。事後誰也說不清自己究竟牽走了幾只,但那天下午三個人都沒有意見。
難的是另一些情況。羊今年要交上去一部分,交多少取決於去年欠了多少。羊分散在幾個村子,而收羊的人不在場。收上來的羊還要折成糧食再發下去,折算的比例是別人定的。到這一步,趕成三堆的辦法就不管用了。有人必須把它記下來,而且記下來的東西要能在另一個人手裡,在另一個月份,被讀成同一個意思。最早那批泥板,做的就是這件事。
先想象兩份記錄。下面是說明記數方式的示意場景,不是兩塊已有明確編號、可以逐一指認的實物。
把時間放在前3300年前後的烏魯克。一塊掌心大小的泥板,上面壓著記號。它記的是一批牲畜,有多少頭,寫在上面。
另一份記錄來自同一座城、同一個時期,記的是一批大麥的容量。今天的人容易預期,記錄人只要換掉商品名稱,仍可使用同一套通用的數字。但當時不能這樣簡單地套過去。
不是有人寫錯了,也不只是同一套數字換了字體。點清牲畜和量一批大麥,當時可能進入兩套不同的數值系統。
這聽起來像個筆誤,但它是當時書寫系統的基本構造。烏魯克的書吏手裡沒有一套脫離對象,放到哪裡都通用的數字。他有好幾套。人和牲畜這類可以一個一個點清的東西,走一套系統。穀物的容量,走另一套。土地面積,又是一套。長度還是一套。某些穀物製品和口糧甚至有自己專門的進位方式,和普通的點數系統並不是同一種字體的兩種寫法,而是兩件不同的東西。
後果是,一個符號的值取決於它正在數什麼。把它從牲畜那一欄原樣抄到穀物那一欄,得到的不是同一個量。要讀懂一塊泥板,得先知道板上那批東西屬於哪一類。類別不清,數字就懸著。
這不等於書吏永遠換算不了。單位之間有關係,關係可以學。真正的意思是,換算不是從數字內部長出來的,是從外部加上去的。這些記號的讀法,還沒有完全擺脫所計對象與單位的約束。
這帶來一個很實際的後果。一塊泥板一旦離開產生它的那間屋子,就可能變得讀不出來。記錄的人知道自己在數什麼,所以不必寫下來,而沒有寫下來的那一部分,恰恰是讓數字有值的那一部分。後世研究者面對一塊沒有出土層位的板子時遇到的困難,有一半是當年那個書吏省下來的功夫。
也不該把這套安排讀成粗糙。它是貼著實物長的。穀物的容量單位跟著實際的容器走,面積單位跟著地塊的丈量方式走,每一套都在自己那一攤事情上順手。一個牧人清點羊群和一個倉吏收穀子,本來就是兩種動作,兩種動作各自積累出一套記號,一點也不奇怪。
從使用的角度看,分開甚至更省事。倉吏一輩子只跟容量打交道,不需要一套能同時數羊的符號。每一套系統都砍掉了自己用不上的部分,有時反而比通用系統更順手。麻煩只在兩套東西要對起來的時候才出現,而那種時候在一個村子里並不多。
要對起來的時候在一座城裡就多了。城裡有倉,有神廟,有工程,有一年到頭的進出,誰欠誰多少必須放在一起看。那些互不通約的記號後來被壓進同一套東西,壓力來自這裡。奇怪的是後來它們被壓進了同一套東西,而那件事要再等一千多年。
現存最早的這批泥板上,記的幾乎都是誰交了多少,還欠多少,發給了誰。它們不是為了留給後人看的。它們是為了下個月還能查得清。
二 最早的書寫里,五分之四以上是賬
原始楔文材料今天通常談到六千塊左右的泥板與殘片,其中約五千件出自烏魯克本身,另有一部分來自傑姆代特納斯爾等受烏魯克書寫傳統影響的地點。按傳統分期,這批材料橫跨約前3350年至前3000年。
尼森對這批最古老文本做過一個經典統計。經濟與行政記錄約佔百分之八十五,詞彙表一類的非行政文本約佔百分之十五。而且那百分之十五主要是在較晚的階段才增長起來。在更早的層位里,詞彙類文本極少,行政登記幾乎是壓倒性的。
所以如果問,今天實際拿到手裡的最早的書寫,賬目佔多少,答案不是過半,是絕大多數。
這些賬目不是後世意義上的簿記,多半是短記錄,一個數量符號,一個商品或人員符號,一個機構或個人的標記,拼在一起。當時的書寫還沒有發展到能自由記錄完整口語的程度,數量,單位和物類反而比句法更清楚。也就是說,這套系統最擅長表達的,是多少什麼給了誰。除此之外它一時還說不了太多。
人名也是跟著賬進來的。烏魯克的十八塊板子上,反復出現同一對符號,讀作庫辛,跟大麥和釀酒用的糧食寫在一起,其中一塊記的是三十七個月裡經手的大麥總數。庫辛是一個人,一個職位,還是一個機構,不知道:這對符號前後幾乎沒有別的字。常見的一種解讀是把它當成一個人。如果是,那麼今天讀得出來的最早的一個人名,是一筆大麥賬上的名字。
這裡必須停一下。百分之八十五說明的是幸存下來的那一批。泥板特別適合保存行政記錄,尤其是被丟棄後曬乾,或者被一場建築火災意外燒硬的那些。而大量一次性的標記,木頭,纖維,口頭指令,以及反復揉掉重來的練習,不會以同樣的概率留下來。從成品檔案的比例,倒推不出發明者當初唯一的動機。
這個區別看上去瑣碎,卻決定了後面所有的話怎麼說。行政需求是書寫成形的核心環境,這一句站得住。會計是書寫唯一的原因,這一句站不住。兩句之間隔著的不是證據的多少,是證據能承擔的重量。
尼森,達梅羅,英格倫德的說法比較謹慎,最早文字的成形與城市機構越來越複雜的資源管理緊密相連。這句話和人類為了記賬發明了文字,差著一大截。前一句是環境,後一句是動機,而動機沒有留下任何一份前3400年的自述。
同一個區別也出現在籌碼上。近東從新石器時代到城市化時期確有大量小型黏土幾何體,圓錐,球,圓盤,還有把它們封起來的泥球和帶外部壓印的容器。施曼特貝瑟拉據此提出過一個長達數千年的連續譜,簡單籌碼對應商品數量,複雜籌碼對應更複雜的物類,籌碼裝進泥球,再壓在球面上,最後二維壓痕取代三維實物,於是有了書寫。
實物是真的。泥球里確實裝著籌碼。但這條鍊子後來被逐段拆過。形態相似不等於功能和語義的連續。分類分得過於整齊,很多籌碼根本沒有明確的會計出土語境。籌碼形狀與最早文字符號之間的一對一對應,也不像那個強說法要求的那樣成立。至今沒有足夠的證據,把整個史前的這一類對象統一解釋成會計裝置,許多東西可能本來就是多用途的。
現在比較常見的處理是這樣,部分籌碼,封泥和數值壓印屬於會計技術的譜系,這個弱版本接受度不低。一個持續數千年,意義穩定,能夠逐個導出文字的統一代幣體系,不是共識。
三 人變成工日
到了烏爾第三王朝,情況完全不同了。這個王朝留下的行政文書,單是已知的就在十二萬件的數量級上。
這些文書裡最能說明問題的一類,是核賬或者平衡賬。它不是一張簡單的收支表,而是把一個責任期拆開來算。先是應交或應完成的總額,然後扣掉合法支出,損耗和已完成量,相減得到差額,差額再判為結餘或者虧空,最後是日期,負責人和核賬說明。
關鍵的一步在於折算。勞動力被換成工日。糧食,羊毛,紡織,農業作業,也都能按規範生產率折成可比的量。烏瑪等地的文書顯示,人員通常按工頭或監工來組織,而行政這一端關心的不是今天來了幾個人,是這支隊伍按規矩應該交出多少個勞動日。
於是賬目的中心站著的不是工人,是監工。
折算這一步做完之後,有些東西就看不見了。一個人今天病著,一個人手腳比別人慢,一個人乾的是最重的那一段,在工日這個單位里全都一樣。賬目並不否認這些差別,它只是沒有給這些差別留位置。能進入總賬的只有一個數,而這個數一旦進去,後面所有的加減就只認它。
舒爾吉三十七年到四十年之間有一組記錄,把數百名女性勞動力以及她們的勞動和穀物責任,連續記在一個叫盧烏魯布的人名下,此人是米納爾尼之子。這類檔案說明工頭不是每天點個名的角色,而是一個長期掛賬的責任節點。賬戶以負責人的名字連年出現,後世的學者才有可能把責任會計這套東西重建出來。
虧空可以結轉。不足的部分作為欠額留到下一期,超出的部分記為盈餘,下一張總賬可以把上一期的餘額吸收進來。一個人的名字因此可以在賬面上背著一筆數字走好幾年。
總賬背後還壓著一層東西。收據,帶封印的憑證,小額單據,在核驗之前一直保留著。核賬做完,它們的證明價值才改變。烏爾第三王朝甚至形成了保存這些支持泥板的容器傳統。所以一份平衡賬不是一塊泥板,是一塊泥板加一筐泥板。
有一個說法流傳很廣,說某個工人死後,他沒完成的定額會轉給家屬。這條得停下來。確實有文書記錄死亡,人員替換,也確實有死者家屬或孤兒的配給。也確實有工頭賬戶結轉虧空。但把這兩種證據合起來,變成死者把勞動債傳給兒子,目前找不到一塊泥板同時寫明某人死亡,尚欠多少工日,該欠額轉予某某親屬。站得住的只有一句:這套會計可以讓賬戶中的虧空跨年度存續。至於個體工人的未完成定額是否在他死後按繼承規則轉為家屬債務,沒有直接實證。
這一條之所以容易滑過去,是因為它太順手了。一個能把活人折成工日的系統,順著想下去似乎理應把債也折給兒子。推理很漂亮,材料卻沒有跟上。系統做得到的事和系統實際做過的事,中間隔著一層,這一層在沒有證據的時候不能自己填上。
同樣,監工對虧空負責這件事基本成立,但那是一個行政責任賬戶掛在他名下,不等於後世民法意義上的個人無限債務。盧烏魯布名下的數字是不是真要他從私人財產里補齊,證據還不夠。他是米納爾尼之子,這一點泥板上寫著。他家裡有什麼,泥板上一個字也沒有。
不管怎麼說,有一件事是清楚的。到這個時候,一個南方城邦的行政系統已經能夠把幾百個活人,他們一年的力氣,他們吃掉的糧食,全部換算成同一種可以相加相減的東西,並且把結果掛在一個人的名字下面。
四 抽象層
第三千紀後期開始,特別是在烏爾第三王朝,可以看到另一個方向上的動作。書吏越來越多地先把具體的度量轉換成抽象的六十進制位值數,在這個抽象層上運算,算完再轉回實際單位。
這裡要把兩件事分開。以六十為重要進位節點的計數傳統,在烏魯克時代就已經存在。但真正把數字從商品單位里抽出來,讓同一組符號按位置表示不同的六十次冪,是第三千紀後期才清楚出現的,烏爾第三王朝進入運算實踐,到古巴比倫的學校完全成熟。支撐這個抽象層的,是表。
古巴比倫的標準倒數表並不把從一到五十九全部列一遍。它主要列那些在六十進制里有有限倒數的數,一張典型的表大約二三十行。至於那些沒有有限倒數的數,表裡乾脆不列。需要的時候可以分解,近似,或者換別的算法。乘法表則把某個關鍵數與一系列乘數的結果逐行排開。度量衡表負責把傳統的長度,面積,容量,重量單位,換成抽象的六十進制量。學生實際運算的核心技巧,可以概括成一句話,除法變成乘以倒數。先在背熟或查到的體系裡找到除數的倒數,再乘上去。所以這些表不是附帶的參考物,是計算本身賴以進行的地基。
對一個學生來說,這意味著他要背的東西和他會做的事情是同一件。背下一張倒數表,他就能做除法。背不下來,他手裡那些數字就不動。技藝裝在記憶裡,而記憶要靠一遍一遍在泥上重來。學校留下的板子里表格佔了那麼大一塊,原因就在這兒。
這套位值數有一個醒目的缺口。早期通常沒有固定的小數點,也沒有後世意義上的內部零符號。同一個書寫形式,理論上可以相差六十倍,三千六百倍,或者六十分之一。書吏靠問題裡的單位,數量級和語境,把絕對值恢復出來。也就是說,尺度不寫在數字內部。
目前也沒有找到一塊泥板,能證明某個書吏因為沒有零而明確算錯,且排除得掉抄寫錯位一類原因。缺口存在,但它似乎並沒有把人絆倒。
換個說法,這套記法把一部分工作留在了板面之外。數字負責相對關係,人負責記住這批數說的是穀子還是銀子,是一整倉還是一天的口糧。它不是一套自足的系統,是一套需要有人在旁邊看著的系統。
統一髮生在哪一層,這一點要緊。沒有哪個國王一夜之間廢掉所有單位。容量,重量,長度,面積仍舊各有各的單位,商人和倉吏照舊用它們。被統一的是計算的那一層,各種單位都能通過標準換算表映射到同一個抽象體系裡去。度量衡表就是這兩層之間的那道門。
現代文獻有時把這一輪標準化簡稱為舒爾吉改革。這個標籤方便,但沒有一塊可以相當於近代度量衡法的舒爾吉詔版,逐條宣佈從今日起某個單位等於多少。能說的是,舒爾吉漫長統治下的這個國家顯著推進了度量,稅役與賬目的標準化。具體哪些單位關係由國王親自下令確立,是由後來一致的文書制度倒推出來的。
關於舒爾吉本人,倒是有一段極好用的材料,而且必須降級使用。舒爾吉贊歌里,他自稱少年時進過學校,學過蘇美爾和阿卡德泥板的書吏技藝,能熟練處理減法,加法,計算和會計。另一篇贊歌稱他是有知識的書吏。問題在於,現存的贊歌抄本主要是古巴比倫時期的學校抄本,大約在舒爾吉生活的年代之後二三百年才寫下來。它們可能保存了宮廷贊歌的傳統,但不能證明歷史上的舒爾吉少年時真的坐過那樣的課堂。今天通常把它當作王權意識形態和理想博學君王形象的證據,而不是一份履歷表。
一個國王願意讓人把會記賬寫進自己的頌詩,這件事本身已經說明了不少。
五 一棟房子裡的一千四百塊泥板
尼普爾有一處民居,發掘者按字母順序給同一片街區的房子編了號,它排在靠後的位置。這棟房子裡發掘出的泥板與殘片約一千四百二十五件,其中百分之九十以上是書寫練習。這一點讓它和大量來路不明的數學泥板完全不同,這裡可以把教材放回一棟真實房屋的房間和廢棄層里。
練習板的形式本身就很有畫面。有一類板子,正面一欄保存教師寫下的範本,旁邊是學生的複製區,背面可能抄一些較長,較早學過的材料。另有一種小圓板,教師先寫一行,學生在旁邊重復。學生的練習區經常被抹平,重新利用。
一塊板可以用很多次。這件事在當時是省錢,在今天是損失。學生練過什麼,錯在哪裡,改了幾遍,大部分隨著那一層被抹掉的泥一起沒了。留下來的是他最後沒來得及抹掉的那一次,或者是他終於寫對之後擱在一邊的那一塊。
泥板的手感差別很大。耶魯那塊編號七二八九的圓板直徑約八釐米,一隻手掌就能托住。大英博物館編號一三九〇一的那塊約十九點四釐米寬,十一點七釐米高,已經需要兩只手或者一張桌子。寫錯了怎麼辦,趁濕用手指或工具抹平,重寫。泥板一旦徹底乾透,就沒有那麼容易改了,所以正式的板子上常常能看到重刻,擠字,局部擦抹留下的不平整。
課程的順序是重建出來的。廷尼,羅布森,韋爾德惠斯等人根據板型,文本組合和抄寫方向,拼出了尼普爾的基礎序列。先學怎麼做楔,怎麼寫單個符號,隨後是一類符號練習,接著抄音節序列,再進入人名列表和按類別排列的詞彙表,然後是更複雜的詞彙系列,計量表,數字與表格。基礎訓練完成之後,學生開始抄王贊歌,格言,爭辯文學和神話。
這個從第一天到最後一天的說法要留一個注腳。手上有的是考古學重建的序列,不是一張古代的課程表。學生可能重復,可能跳過,可能並行練習。一棟房子的材料也不該無條件推廣成整個巴比倫的教育制度。羅布森本人對這種推廣就很警惕。
古巴比倫文學里有一類後來被稱作學校生活的對話文本,而且它們就是學生要抄的材料。其中一篇從早晨寫起。學生拿著泥板去學校,朗讀自己那一塊,吃午飯,準備新板,回家之後還要在父親面前把當天的東西復誦一遍。
第二天上午,教師檢查他的板子,發現有地方缺了。棍杖第一次落下來。
接下來的事情才是這篇文本真正的樣子。管功課的人打他,說了什麼,泥板上殘了。管院子的人打他,問他為什麼趁自己不在就說話。又有人打他,問他為什麼不把頭抬好。管畫圖的人打他,問他為什麼從座位上站起來。管門的人打他,問他為什麼走出了門。又有人打他,問他為什麼拿了一樣東西,那樣東西的名字殘了。管蘇美爾語的人打他,因為他在該說蘇美爾語的時候張口說了阿卡德語。最後是他自己的老師,說他的字寫得不好。連早上那一次算在一起,一天之內九次,理由一條比一條更細。
當天晚上,這個孩子的父親把那位教師請到家裡,端上酒和食物,又送了衣物。教師喝完酒,轉過頭來稱贊這個學生。
這一幕好用得幾乎讓人不想去核。所以要馬上說清楚,它來自學校文學,不是當天的紀律記錄。這類文本產生於古巴比倫時期,不像後面要談的那位希臘人那樣晚了一千年,但體裁仍然是文學。連續挨打和請客宴飲可能利用了真實的制度,不能證明每所學校每天如此。
泥板形態能夠獨立支持的是另一部分。教師範本和學生抄本確實並排存在,學生區確實有重復,磨掉和重寫,高級學生確實抄文學。教師示範,學生模仿,檢查糾錯,這條線很穩。
烏爾另有一處房子,門牌被現代發掘者記作安靜街七號,出土兩千餘件文書和練習材料,屬於庫寧伽爾一家。常見的標籤說這是一個世襲書吏家族,這個標籤得改。庫寧伽爾和他的幾個兒子有淨禮祭司的身份,家中進行教學是可靠的,說他們整個家族的主業就是書記員則過度簡化。可考的人物包括他的兒子烏爾南納,印章上稱他為與月神相關的祭職人員和檔案負責人。
至於是不是世襲,最好的回答是有強烈的家族連續性,但沒有法律意義上的封閉資格。識字技術,泥板收藏,人脈和官職資源集中在家庭里,自然形成優勢,而姓名和職銜的變化又說明並不存在一個固定的書記種姓。報酬也沒有統一的工資表,糧食,羊毛,土地收益,口糧以及職務本身都可能構成收入。從書吏受尊重推不出每個低級抄寫員都富裕。
學校面向平民天才開放,識字因此成為社會上升階梯,這個說法的直接證據很弱。現有的學生檔案明顯偏向那些已經握有行政和祭司資源的家庭。一個普通農業家庭的孩子進入高級書吏訓練的概率是多少,算不出來。
六 沒有出口的題
大英博物館那塊編號一三九〇一的泥板,四欄,二十四道關於正方形和矩形邊長與面積的題目,從簡單向複雜排列。它不是科學發掘出來的,沒有安全的出土層位。
把這二十四道題讀一遍,有幾件事很難忽略。它們排成了一個梯度。同一個操作被反復變形。數字被挑得異常整齊。
排成梯度這件事需要有人來做。第二題比第一題難一點,第三題又難一點,這個順序不會從任何一筆賬裡自然長出來。它要求有人先想清楚哪一步是關口,再造出一批只在那個關口上有差別的題。造題的人心裡裝的不再是某一塊地或者某一倉穀子,是學生會在哪裡卡住。
這類題目往往穿著行政的外衣。田地,磚塊,溝渠,勞工,銀子,糧食,這些是書吏職業世界裡的標準對象,出現在題面上再自然不過。但沒有哪個糧倉管理員會在工作中遇到這樣一道題。給定的尺寸是為了讓程序跑得順,不是為了讓某塊地被丈量。
耶魯那塊圓板也是同一類東西。直徑八釐米,一隻手就能拿,出處不明。正面畫著一個正方形和兩條對角線,一條邊上寫著一個數,對角線附近寫著兩個數,其中一個是正方形對角線與邊之比的極精確值。背面有一部分被抹掉過。常數表裡保存著同一個對角線常數,所以這個學生很可能是在使用一個已知的常數,不一定是當場把它算出來的。
這塊板證明的是古巴比倫人能夠以很高的精度處理正方形對角線的關係。它不證明他們擁有希臘式的命題與演繹體系。用後世的定理名字去稱呼它,是把一整套知識組織方式偷偷塞了進去。
爭議最大的是那塊普林頓三二二。它寬約十三釐米,高約九釐米,厚兩到三釐米,沙黃色,表面有鐵鏽橙和黑色的斑駁,還有明顯的刮痕,邊緣殘損。現存四欄,十五個完整數據行,左側原來可能還有缺失的部分。
它的來路可以一步一步排出來。喬治普林頓大約在1922年至1923年間從一個古物商手裡買下它。賣方說來自森克雷赫,也就是古代的拉爾薩,但沒有科學發掘記錄,所以這個出土地不能升格為確定的層位。二十世紀三十年代,它隨普林頓的藏品進入哥倫比亞大學。
1945年,諾伊格鮑爾與薩克斯認出表上的數值與直角三角形的邊長關係相合。這個數學結構可以檢驗,從來沒有爭議。有爭議的是它是什麼。
後來有作者把它稱為三角函數表,甚至稱為世界上最早的三角函數表。羅布森在2001年到2002年的重新分析反對這種讀法,理由是古巴比倫文獻裡沒有與後世角度函數表相當的概念體系,而倒數對,學校乘法表,問題生成和表格格式,都有大量本土的平行證據。她據此把它解釋成教師用來準備直角三角形題目的一張工作表。2017年又有人重新提出精確六十進制三角學表的強說。
比較穩妥的裁定仍然是,泥板與直角三角形關係,倒數對以及學校問題生成密切相關。把它叫作三角函數表,需要引入古巴比倫材料自身沒有提供的概念。
這類命名問題不止一處。原始的泥板上沒有符號方程。它們用阿卡德語的動詞描述操作,長度,寬度,使其相持,撕去,附加,組成正方。二十世紀三十年代到四十年代,諾伊格鮑爾與蒂羅多丹第一次大規模破譯這批文本,並用現代代數把程序壓縮成方程。這一步在揭示數學結構上極其成功,卻帶來一個副作用,讀者容易把方程當成古代書吏腦子裡實際存在的對象。許律普後來從語言出發重讀,認為那些看似解二次方程的操作,本土語義往往指向可測線段和面積的拼接,切割與補形。今天通常承認兩種現代語言都能把結果形式化,但要問書吏自己在做什麼,語文學的重建更貼著詞彙證據。
回到那二十四道題。它們不是賬目,不會進入任何一筆結算。同一批房子裡,同一批手裡,產出的東西已經分成了兩種。一種最後要交上去,另一種交給誰都沒有用。
這兩種東西共用一套詞彙,共用一套記號,甚至共用同一批泥。區別只在出口。前一種走進倉庫和王室,後一種走進另一個孩子的手裡。而後一種一旦開始生產,就有了自己的節奏,它按難易排序,不按收成排序。這個節奏一旦立住,就不再需要外面有人下令。今年的收成好不好,不影響第二題該不該比第一題難。
不能給出一個百分比。用途不是目錄上可以直接清點的物理屬性,一張倒數表既是學校練習也可能服務於未來的會計,一道田地題可以完全虛構而訓練的是真實的職業技能。可以可靠引用的是數量級,已知的數學楔文文本約兩千件,其中約一千件已有轉寫和翻譯出版,另有大致相同數量還在等待整理。這兩千件里,乘法表,倒數表,平方與平方根表,計量表和學校題目佔了很大一塊。
整套記賬的手藝是為了清點而立起來的。等它站穩,它已經開始生產一些不清點任何東西的東西,就在同一批房子裡,出自同一批手。
七 尼羅河那邊
埃及的情況先要說一個數量上的落差。整個法老時期及其後,能夠算作專門數學文本的材料大約二十五件,現存問題約一百道,其中絕大多數集中在兩捲紙草上。相比之下,楔文數學文本已知約兩千件。
理解這個落差,保存條件是不能繞開的原因。黏土即使只是晾乾也能長期存在,一場建築火災還可能把它燒得更硬。紙草,皮革和木板一旦進入潮濕的土層就極易腐爛,而尼羅河谷和三角洲的農業官署,恰恰處在最不利於有機物保存的位置。把二十五和兩千放在一起比較兩地的數學活動,比較的其實是土壤。
最重要的那一卷叫萊因德數學紙草。它現在分成幾段,大英博物館的第一段長約二百九十六釐米,高約三十二釐米,第二段長約一百九十八點五釐米,同樣高約三十二釐米,另有若干碎片在布魯克林。兩大段加起來已近四點九五米,加上碎片和失落的接縫,原卷展開超過五米。它不是一本可以翻頁的冊子,是一條比普通客廳牆面還長的窄長捲軸。
卷首署著抄寫者的名字,阿赫摩斯。他在開頭宣稱此卷提供一種準確計算,用以探究事物,認識各種奧秘的知識。隨後明確記年,說抄寫於上下埃及王阿佩皮三十三年。又說自己依據一份古老的抄本,那個舊本制於尼瑪特雷時代,也就是通常認定的阿蒙涅姆赫特三世。
舊本已經不存在了。關於它的直接證據,只有阿赫摩斯本人在大約三百年後的這一句說明。他是逐字複製,節選,更新了數據,還是拼合了多種材料,無從檢查。今天通常接受他自述所保存的傳統年代,但也只到這一步。
抄寫在當時不是次一等的工作。一份東西能被抄,說明有人認為它值得再存在一次,而抄的人有機會決定哪些留下,哪些不留。阿赫摩斯留下了一個名字和一個年份,這已經比同時代絕大多數握筆的人多。埃及人自己怎麼勸孩子去做這一行,有一篇文字說得很清楚。
它的框架是一位父親帶著兒子上路,一路上把別的行當挨個數落過去。木匠累得直不起腰。泥瓦匠身上糊滿了泥。洗衣工整天泡在水裡,鄰著鰐魚。漁夫,箭匠,信使,一個也沒放過,每一種都被寫得又髒又苦又沒有指望。數落完一輪,父親把結論重復一遍,沒有哪一行比得上書吏。
這不是一份職業收入調查。它形成於中王國的傳統,但現存的完整抄本和大量學校抄件主要來自新王國,也就是說,後來的孩子一代一代抄寫的是一篇勸人當書吏的文章。今天有人把它讀作諷刺,有人更願意稱它為書吏行業的宣傳。兩種讀法都不把它對其他行當的描寫當成實錄。
不過有一點它沒說謊。寫這篇東西的人和抄這篇東西的孩子,是同一群掌握記號與數字的人。
新王國晚期還有一卷學校用的抄本,今天叫蘭辛紙草,藏在大英博物館,勸法一樣,數落到農夫那一段寫得最細。書吏在河岸下船,來查收成,身後跟著拿棍杖的隨從和拿棒子的努比亞人。有人對農夫說,交糧。農夫說,沒有。於是他挨了一頓狠打,被捆起來扔進井裡,妻子被綁,孩子戴上了腳鐐。整卷翻來覆去落在同一句勸告上:去當書吏。這仍然是勸學的課文,不是一份催糧的記錄。課文里下船查收成的,正是它勸孩子去當的那種人。
再回到萊因德數學紙草,它的出土來歷同樣不清楚。萊因德在1858年於盧克索購得主要部分,賣方說來自拉美西姆附近,沒有經過記錄的科學發掘。他死後,大英博物館在1865年前後獲得主要卷。史密斯在十九世紀六十年代又在盧克索買到一些碎片,後來發現能與萊因德卷拼接,他的女兒在1906年把它們捐了出去。其餘的埃及數學材料,來路和形狀各有各的怪。
莫斯科那一卷長約五米,高卻只有四到八釐米。它不是一張紙,是一根帶子,上面擠著二十五道題,從糧倉算到面積,還有一道算截去頂部的方錐的體積。戈列尼謝夫在1893年從古物市場買下它,同樣沒有出土地點。
還有一件東西不是紙草。那是一卷皮革,約二十五釐米乘四十三釐米,上面寫著好幾組等值的單位分數分解。它跟著萊因德那批材料進了博物館,然後就一直卷著。皮革乾透之後又硬又脆,強行展開等於毀掉,沒有人敢動。它躺了將近七十年,直到1927年才被處理開來。
與前面幾件購自古物市場的材料不同,拉罕的那一批來自有記錄的發掘。皮特里在一座中王國城市裡挖到它們,因此這一批有明確的考古語境,知道是從哪座房子,哪一層里出來的。數學只是那批紙草中很小的一組。
埃及書吏處理非整數的方式很有特點。一個不足整數的量,通常被寫成若干個不同的單位分數之和。萊因德卷開頭有一張大表,專門把一類分數拆成可以操作的組合,覆蓋到相當大的分母。它的用途不是欣賞分數的性質,是幫書吏在倍增,配給和除法里處理那些沒法靠簡單對折得到的份額。卷子後面關於糧食,麵包,啤酒和勞工分配的題目,不斷調用同一套習慣。
拉罕那一批里就有一份同類型的較小的表。它比萊因德卷更早或同期,出土層位清楚,因此萊因德卷上那張大表不是孤立的發明,是一個傳統。
這套體系讓倍增,二等分和把份額寫成標準可識別的部件變得很自然,也容易和容量單位配合。代價是某些量會變成多項之和,而選擇哪一種分解需要訓練和查表。稱它笨拙則是拿後來的記法去量它。沒有哪個埃及書吏留下過抱怨這套體系麻煩的文字。現存的錯誤,修正和輔助表能證明操作需要技巧,不能證明操作者本人覺得它低效。
埃及也有不通向任何賬目的題。最醒目的是萊因德第七十九題。
七座房子。每座房子裡七隻貓。每只貓盯著七隻老鼠。每只老鼠啃著七穗穀物。每穗穀物又能收出七份量器的糧。數量就這樣一層一層翻上去,越翻越荒唐,最後要問的是全部加起來一共多少。
糧倉管理員一輩子也撞不上七座房子裡正好各有七隻貓。這道題的房子,貓和老鼠不是為了記錄什麼,是為了讓一個學生把七的冪一層層算下去而擺在那裡的。三千五百年前有人坐下來編了一個笑話,並且把它寫成了作業。和兩河那邊一樣,埃及的題目裡也有大量數據被刻意挑得非常適合程序運算,題目使用糧倉,與題目是一次真實的糧倉記錄,完全是兩回事。
萊因德第五十六至六十題討論一個叫塞克德的東西,用每上升一肘對應多少水平方向的手掌寬和手指寬來描述斜面。換成後世的語言這是坡度,但原文不用角度,也沒有三角函數。
古王國的建築工程另有極強的第一手證據。瓦迪賈爾夫出土的梅雷爾日誌屬於胡夫晚期,原文紀年為第十三次牲畜清點的次年,通常折算為在位第二十六或二十七年。梅雷爾手下是一組四十來人的船工,這樣的組一共四個,合成一支工隊。日誌記著他們從圖拉運石灰石,走水路送往吉薩胡夫的工程區,日期,人力,調配都在上面。
梅雷爾本人不是數學家,也不是後世意義上的工程師。他是一個監督員,手下四十來人,要按日子把石頭運到地方。日誌之所以重要,是因為它顯示這樣一件工程需要多少種記錄才轉得動,而每一項記錄背後都要有人會算。會算的人不一定寫過一道題,寫題的人也不一定押過一趟船。採石場痕跡,工隊標記和工人聚落也都在,工程的組織程度沒有疑問。
但沒有一張胡夫時代的坡度計算表留下來,而萊因德卷比胡夫晚了將近一千年。金字塔的實際坡面確實可以用後來的塞克德單位倒算,某些坡度還落在很整齊的掌與指的關係上,說古王國的建築師掌握某種等價的坡度控制技術,非常合理。但從實測值反推他們就是照萊因德第五十六題那個程序設計的,仍然是推斷。研究古埃及建築圖的學者提醒過,許多幸存的草圖並不是後世意義上的比例施工圖。
埃及的容量計量另有一套單位,一個叫赫卡特的量再一路對折下去,在糧食,配給和容量換算里真實存在,萊因德卷裡有題目專門演示這些單位怎麼互換。這套對折分數後來會引出一個極漂亮的說法,那個說法留到後面處理。
阿赫摩斯的名字留在卷首。他沒有說自己是數學家。那個詞還要等很久才被造出來。他說自己是抄寫的人。
八 我認為
關於幾何學的起源,流傳最廣的一個故事來自希羅多德。
在他的記述里,埃及的一位王把土地分成相等的方塊,按年徵租。如果尼羅河衝走了某人的一部分土地,國王就派人去測量剩下的面積,相應降低租額。然後希羅多德加了一句,大意是,我認為幾何學就是這樣被發現的,後來傳到了希臘。這個故事有兩處需要處理。
第一處是時間。希羅多德寫作於大約前五世紀中葉。如果他筆下那位王背後主要投射的是中王國的傳統,那麼他距所述的王權時代約一千三百到一千五百年。即使把故事理解成一般的古埃及制度,他也比萊因德卷所屬的那個傳統晚了一千年以上。
第二處更要緊。他自己標了。我認為這三個字就在原文裡。希羅多德把因此發明幾何寫成了自己的解釋,不是埃及檔案裡的原句。後來的傳抄者做的事情,是把那三個字去掉。
三個字的差別在這裡很大。帶著它,這是一位旅行者對自己所見所聞的推論。去掉它,這就成了一條關於起源的記載。後一種形態更好記,也更好用,於是它走得更遠。
埃及人測地這件事本身沒有爭議。面積問題,地塊記錄,拉繩的測量活動,稅租文書,全都存在。缺的是任何一份埃及本土的文件寫道,洪水抹去了地界,因此我等發明了幾何。
故事後來還長胖了。打了十二個結的繩子,用三四五的邊長關係重新定出直角,這些細節連希羅多德那裡都沒有。它們是近現代數學史裡長出來的。
把兩件事排在一起看,會發現一個次序。希羅多德那句推論寫於前五世紀。十二個結的繩子是近現代長出來的。越往細處看,故事的年紀越輕。還有第三個,比前兩個都年輕。前面提到埃及的容量單位一路對折下去。有一個說法把這些分數講得極漂亮。
荷魯斯與塞特爭鬥,一隻眼睛被撕碎。碎片散開,每一塊對應一個對折下去的分數,二分之一,四分之一,八分之一,一直到六十四分之一。把碎片全部拼回去,差一點點才是完整的一隻眼。差的那一份,由智慧之神托特補上。這個故事好到幾乎不必核對。分數,神話,缺口,補足,一樣不缺,而且缺的正好是最小的那一份。
里特追查過它的現代生成史。中王國早期的容量分數符號主要是僧侶體的書寫符號,沒有哪份古代文本說它們是眼睛的部件。真正把這些符號畫成眼睛各部分的強版本,是二十世紀初的符號比較里逐漸形成的,二十世紀二十年代經由加德納和數學史教材傳播而成為經典。
荷魯斯之眼被損傷又被修復的神話當然古老。六個碎片對應六個對折分數這件事,最早的明確陳述來自現代埃及學,距那個時代約三千五百年。三個故事,一個比一個年輕,而講的都是三四千年前。
這個故事還有一個特點,不容易注意到。它沒有主角。它講的是埃及,不是某個埃及人。這一段時間留下的名字太少,少到一個關於起源的說法找不到人可以掛,只好掛在一整條河上。
同一類問題也出現在尼羅尺上。埃及很早就記錄泛濫的高度,古王國的王室年代記錄傳統里就有年度水位數據。後世實際的尼羅尺有柱式,階梯式,井式多種構造,刻度用肘。水位與農業潛力當然高度相關,太低意味著可灌溉的土地不足,太高又會造成破壞。國家知道水情,據此估計收成並調整徵收能力,是很合理的重建。
但在這個時段裡,沒有保存下來一份可以寫成水位多少肘等於稅率多少的法老時代稅則。把尼羅尺讀數與稅制緊密連接的詳細證據,在托勒密,羅馬尤其伊斯蘭時代要豐富得多。今天著名的羅達尼羅尺,本身是公元861年的建築。宏觀上的關聯可信,精確的機械換算不屬於這個時段。把視線從故事挪回記錄本身,會看到另一件事。
已發現的楔文書寫物通常估在五十萬到一百萬之間,到2016年時已有三十萬余件被編目。其中數學類約兩千件。烏爾第三王朝的行政文書單獨就約十二萬件。而埃及的專門數學文本約二十五件。這個分布至少帶來四種系統性的偏差。
最廉價,最頻繁的那部分學習過程,恰恰最不容易保存。日常的濕泥練習被抹掉了,只有被丟棄後曬乾或者意外燒硬的板子進入了考古記錄。埃及的洪泛區幾乎完全沈默,而沙漠墓地和荒漠邊緣的聚落更容易留下東西,於是現代看到的樣本偏向宗教,墓葬和少數乾燥地點。高級文本比日常常識可見得多,一個農民,商販或者工頭怎麼心算,怎麼打結,怎麼用容器目測,怎麼口頭記債,通常不會留下他自己的記錄。學校本身大量依賴記憶和口授,教師範本,學生抄寫,文學文本裡的朗誦,反復磨掉的練習區,都間接說明口頭教學存在,但課程裡有多大比例是口傳,算不出來。
還有一層偏差與誰握筆有關。書吏世界全是男性這個說法並不成立。女性書吏的稱號至少在阿卡德和烏爾第三王朝時代已有證據,到古巴比倫更加明確,研究者已經識別出若干件由女性在題記中署名的學校文本,從基礎的音節和詞彙練習一直到蘇美爾文學都有。古巴比倫的一個女性群體中有識字,管理財產和書寫文書的實例,阿瑪特馬姆就是常被引用的一位。
與此同時,在烏爾第三王朝的大量賬目裡,女性和奴隸是被計算的人。紡織女工,依附勞動者,兒童,被換算成口糧和工日,掛在監工的名下。兩件事同時為真。
檔案是由握筆的人生產的。所以記錄對其餘人的沈默,是生產檔案的制度留下的偏差,不是一次人口能力調查。因為賬目裡很少見普通婦女和奴隸寫數學板,就說他們不會計算,這個推論方向是反的。
至於最初教人計數的是誰,非書吏家庭的孩子怎麼學會日常算術,有多少算法從來沒有被寫下來,早期埃及建築師完整的設計程序是什麼,烏魯克書寫出現之前的口頭會計是怎麼運作的,這些都不知道。任何用幸存的一兩捲紙草去填滿這些空白的敘述,都是推測。
留下來的泥板,是有人覺得值得留的那些,或者是一場火恰好烤硬的那些。為了下一課而被抹掉的那些,什麼也沒有留下。那個把練習欄抹平重來的孩子,不知道自己正在清除證據。
數還在往下算,而什麼算數學,還沒有算清楚過。
Sources and further reading史料与延伸阅读史料與延伸閱讀
Selected references for historical details and interpretive disputes. Museum records, ancient literary accounts and modern reconstructions do not carry the same kind of evidence.
以下资料对应文中的历史细节与解释分歧。馆藏记录、古代文学与现代重建,不是同一种证据。
以下資料對應文中的歷史細節與解釋分歧。館藏記錄、古代文學與現代重建,不是同一種證據。
- Peter Damerow on Kushim and the origins of writing达梅罗:库辛与书写的起源達梅羅:庫辛與書寫的起源
- Eleanor Robson on the uses of mathematics in ancient Iraq罗布森:古代伊拉克的数学用途羅布森:古代伊拉克的數學用途
- Robson, More than Metrology罗布森:《不只是度量衡》羅布森:《不只是度量衡》
- British Museum: BM 13901大英博物馆:BM 13901大英博物館:BM 13901
- British Museum: Rhind Mathematical Papyrus大英博物馆:莱因德数学纸草大英博物館:萊因德數學紙草
- Robson, Neither Sherlock Holmes nor Babylon罗布森:重新评价普林顿322羅布森:重新評價普林頓322
- Pierre Tallet: the Wadi el-Jarf papyri塔莱:瓦迪贾尔夫纸草出版材料塔萊:瓦迪賈爾夫紙草出版材料