The Underlying Logic of Riichi and Chinese Official Mahjong, Part 4: The Rules System (I)

The Underlying Logic of Riichi and Chinese Official Mahjong, Part 1: Payment Systems

The Underlying Logic of Riichi and Chinese Official Mahjong, Part 2: Winning Requirements

The Underlying Logic of Riichi and Chinese Official Mahjong, Part 3: Design Principles

The preceding articles examined the differences between Riichi and Chinese Official Mahjong, arguing that they chiefly reflect differences in national values and aesthetic preferences, especially in the two core elements of winning requirements and payment systems. Each game has also developed a complete set of supporting provisions around these elements, reinforcing its values and purpose and ultimately forming a logically coherent, structurally complete system.

(I originally planned to cover these supporting provisions in a single article. But the subject proved extensive: halfway through, the draft already exceeded 5,000 Chinese characters. With the past few months also unusually busy, I decided to publish the completed portion first. The discussion is therefore split into two parts: this one covers rules derived from winning requirements, and the other focuses on payments.)

Enhancing enjoyment

Whether played as a tabletop game or for gambling, a satisfactory mahjong ruleset must first be entertaining enough to meet different recreational needs. Mahjong inherently offers enormous replayability: endless combinations, randomly dealt hands, and calls that change the order in which players receive tiles make every hand fresh and unpredictable.

The enjoyment of large hands

Another major source of enjoyment is the enormous variation in rewards. Traditional board games such as Chinese chess and go produce a simple win or loss. Mahjong also distinguishes victory from defeat, but can assign different rewards according to a hand's beauty and difficulty, with large hands worth dozens of times more than small ones. In other words, Chinese chess and go present a black-and-white, zero-sum result, while mahjong is a points game with layers and gradations.

Winning already provides positive feedback; completing a large hand greatly amplifies the pleasure. Imagine how dull the game would be if every win scored exactly the same, as in the simplest basic-hand rules. This variable payment structure naturally suits gambling. But even without that unhealthy form of entertainment, substantial score differences greatly enhance enjoyment in money-free competition and recreation.

Different rulesets have consequently devised many ways to create large hands. Chinese regional mahjong, mostly used for gambling, has evolved an enormous variety of doubling mechanisms; see the discussion of regional mahjong. Even competition-oriented Chinese Official Mahjong retains flower tiles, a purely random source of points inherited from tradition. Since each flower is worth only one point and does not count toward the winning minimum, these are effectively post-win bonuses with little effect on skill or strategy. Removing flowers altogether would not undermine its competitive character.

Dora in Japanese mahjong

Dora has far greater significance in Japanese mahjong than flowers do in Chinese Official Mahjong. Without it, Japanese mahjong would arguably lose almost half its playability. Earlier articles argued that concealment and full-discarder payment fit the Japanese value of not troubling others. Their practical effect is that players avoid calls and rely on the luck of concealed draws, discarding cautiously for fear of dealing in. Riichi introduced some variation, but most completed hands still consisted of small patterns such as concealment, pinfu, and All Simples. Play remained repetitive, and scores changed little.

Against this background, the four copies of a randomly designated visible dora tile add roughly one han per hand per player on average, without favoring any particular player. Red dora adds roughly another han where used. In practice, building around dora increases its actual contribution further. Japanese mahjong uses multiplicative scoring, so one han doubles the score. Dora therefore substantially increases hand values and the chance of making a large hand in point terms. Even a minimal one-han All Simples hand can become mangan with several dora. Visible and red dora greatly increase enjoyment, providing much-needed repair to a system that emphasizes concealment, gives relatively little emphasis to pattern variety, and otherwise makes large hands extremely difficult to achieve.

Originally, dora was visible in advance and had to be present in the winning hand. Players could build and defend around it, and the resulting skills became an important part of Japanese strategy. As riichi spread, new mechanisms developed around the concealed-riichi route: ura-dora and ippatsu. Unlike visible dora, ura-dora is revealed only after a player wins following riichi. It is completely unknown beforehand and cannot guide choices in the same way. Ura-dora and ippatsu chiefly offer the concealed-riichi route the possibility of a higher score and are purely gambling elements. Their overall strategic effect is only to raise the expected return of concealed play relative to opening, a much smaller role than visible dora's.

Historically, dora types and quantities increased. The Road to Modern Mahjong records:

One of the many emerging grassroots rules was “fixed dora.” Its prevalence is unclear, but among police officers, the Two of Circles resembled handcuffs and the Seven of Circles a pistol, so both became dora. In the bicycle-racing industry, the Two of Circles represented wheels. Among parliamentary employees, the Seven of Bamboo resembled the Diet building. One chemical company designated the Three of Bamboo as oxygen and the Seven of Bamboo as nitrogen. Japanese National Railways used the Green Dragon to represent its “Green Window” ticket counters.

Because dora has a strong gambling character, competitive organizations differ over which types to use. The long-established Japan Mahjong League's competitive A rules retain only visible dora, excluding ura-dora, ippatsu, and red dora. Other associations may include ura-dora, kan-dora, and ippatsu, but generally omit red dora. Given the number of types, their frequency, and their enormous influence, calling Japanese mahjong “dora mahjong” would not be unreasonable.

Japanese mahjong's system built around concealment

Open-hand value reduction

Japanese mahjong continually strengthens concealment through mechanisms such as riichi, ura-dora, and ippatsu. It also weakens or restricts open play. The most representative provision is open-hand value reduction, or kuisagari. Certain patterns lose han after the hand is opened through a chow, pung, or kong. Pure Straight, Mixed Triple Chow, and Mixed Outside Hand, for example, are worth two han concealed but only one when open. One-han patterns such as Pure Double Chow and pinfu effectively fall to zero when open, becoming concealed-only patterns.

The idea can be traced to Chinese classical mahjong, whose scores primarily reflected construction difficulty. Pungs were harder than chows, and kongs harder than pungs, so chows earned nothing and kongs twice the minipoints of pungs. Concealed pungs and kongs were harder to assemble than called ones, so they received higher values. Chinese Official Mahjong retains this distinction. In Chinese mahjong, however, the reduction is confined to pung- and kong-related scoring and has not been extended to pattern values generally.

Apart from Japanese mahjong and Japanese-influenced Taiwanese mahjong, almost no rulesets assign separate concealed and open values to the same pattern, as in Taiwan's open and concealed dragon straights. Chinese mahjong encourages building large hands through calls, which it values far more than remaining concealed for its own sake. Nor does it regard an open Full Flush as less beautiful than a concealed one. Extending open-hand reductions to numerous patterns therefore expresses Japan's preference for concealment.

Early Japanese mahjong did not have kuisagari. According to The Road to Modern Mahjong, the Rainbow Conference that established concealment's status occurred in 1929, riichi formally appeared in Shōwa 24 (1951), and open-hand value reductions gradually became established during the Shōwa 30s. This indicates that they developed alongside riichi and related new rules as part of strengthening concealed play.

Modern Japanese mahjong raises concealed-hand scores through riichi, ura-dora, and ippatsu while reducing the scoring power of open hands through kuisagari. This reflects its balancing of the concealed and open routes.

Pinfu and All Simples

Pinfu and All Simples are basic one-han yaku and among the most common patterns applying to the hand as a whole. Yet mainstream Japanese rules allow an open All Simples hand while requiring pinfu to remain concealed: open tanyao is allowed, but open pinfu is not.

Making pinfu concealed-only is understandable. It requires all melds to be chows, a non-value pair, and a win other than on a single-tile pair wait, a structure naturally suited to concealment. All Simples is somewhat harder, yet may be open—a frequent source of controversy, since more complex patterns such as Half Flush and Mixed Triple Chow can also be worth only one han after opening. A tiny “Ron, All Simples, one han” interrupting someone's large-hand attempt has accordingly become an online joke about Japanese scoring.

Whether these two yaku should be concealed-only also concerns the balance between concealed and open play. Tenhou statistics put concealed pinfu at about 20% of winning hands, and All Simples, concealed and open combined, at 22%. In Chinese Official Mahjong, which does not emphasize concealment, both are two-point patterns, but All Chows occurs in about 40% of wins and All Simples in 10%. This is closer to the theoretical ratio of their combination counts, 4.8 × 10¹² / 9.0 × 10¹¹ = 5.2. Under comparable conditions, the frequency ratio is therefore around four to one.

If All Simples were also concealed-only in Japanese mahjong, its winning frequency would fall to roughly 5%. Overall wins and open-hand wins would decline substantially, by about 15%. Since All Simples is a major support for open play, without a replacement this would greatly increase exhaustive draws and upset the balance between concealed and open routes. Thus allowing open All Simples is a necessary choice for practical playability and game balance.

Prohibiting swap-calling

The prohibition on kuikae is another restriction strengthening concealed play. There are two forms: calling a tile and immediately discarding an identical tile, or calling a chow and discarding the tile at the other end of an alternative sequence. For example, with 345 in hand, one calls a 6 and discards the 3.

Both are consistent with mahjong's basic operations. At most, they fail to improve progress toward readiness or a win, and other rulesets rarely expressly forbid them. In some hand-building situations, changing the end of a chow is not merely permissible but necessary. A Mixed Triple Chow or Pure Straight may require 456 rather than 345; calling 6 and discarding 3 is then the required adjustment. Even calling and discarding an identical tile can be a valid defensive way to control risk and avoid dealing in. From both hand-building and defensive perspectives, swap-calling is a reasonable, skillful choice.

Japanese mahjong prohibits it not because of a logical problem, but to protect the concealed-riichi route, particularly ippatsu. Ippatsu awards an extra han for winning within the first uninterrupted turn cycle after riichi; any call cancels it. Since swap-calling often leaves tile efficiency unchanged, it is the easiest and most direct way to interrupt an opponent's ippatsu. The prohibition therefore protects a reward specific to concealed riichi. Viewed within a system that prioritizes concealment and riichi, the restriction is understandable.

Concealment and the emphasis on tile efficiency

Because Japanese mahjong favors concealment, a player must construct the winning hand through entirely random, probability-governed draws, making concealed-hand tile efficiency essential. In its simplest definition, tile efficiency means getting to a win faster. Concealed-hand tile efficiency uses known information—the current hand, visible discards, and so on—to assess the types and quantities of remaining tiles, then chooses the discard most likely to reach a winning structure quickly, without considering pattern value, defense, or deal-in risk.

This is the most basic Japanese mahjong technique: a probability-based decision from known information. Because the objective is to win quickly rather than win bigger or play more safely, narrow tile efficiency excludes patterns, scores, and offense or defense. Advanced strategies that estimate unknown information, such as reading the remaining wall, belong to a higher level beyond pure tile efficiency. Thus tile efficiency is the technique of pursuing the fastest win as the sole objective, ignoring other measures—the technique of racing to win while concealed. This is also the core concealed-hand idea: no reliance on calls or high-value patterns, just optimal draws to win first.

Japanese mahjong's preference for concealment prompted exceptionally systematic study of tile efficiency, a pioneering contribution to the mathematical and scientific treatment of mahjong. However, concealed-hand efficiency is essentially the efficiency of basic-hand mahjong without patterns, defense, or scoring. It is a universal foundation, not something uniquely sophisticated about Japanese mahjong. Once a ruleset introduces many ways to increase scores, decisions cease to pursue only the fastest win; they become a multi-objective optimization balancing tile efficiency, expected hand value, and offensive and defensive risk, with efficiency reduced to one factor among several.

Even in Japanese mahjong, a dora tile may be disconnected from the rest of the hand and disposable under pure efficiency, yet its scoring and defensive significance make it difficult to discard. Dora therefore leads players to sacrifice maximum speed for higher scores or lower risk. It works against pure tile efficiency. The same applies to all scoring patterns and the many doubling mechanisms in regional rules: each reduces the exclusive priority of concealed-hand efficiency.

(Of course, one can define a broader concept of efficiency that incorporates dora and yaku. But this absorbs all mahjong skills into the term, becoming a concept of maximum expected score that combines efficiency, value, winning probability, risk, and other information. Dora is therefore compensatory not only for concealed hand-building but also for strategy: it breaks the single objective of winning quickly and requires attention to score, increasing variety and enjoyment.)

This also exposes a misconception in the frequent criticism that Chinese Official Mahjong works against tile efficiency because it emphasizes scoring patterns and has a high winning threshold. Its eight-point minimum and much larger pattern repertoire make pattern construction more central. Japanese concealed play restricts pattern choices and therefore relies much more heavily on efficient draws. Precisely because Chinese Official Mahjong combines the speed represented by tile efficiency with the returns represented by pattern value, it offers greater depth than a pure-efficiency system pursuing speed alone.

Chinese Official Mahjong's supporting rules for hand-building

Around its central commitment to hand-building, Chinese Official Mahjong provides 81 patterns and numerous construction routes. It also includes supporting provisions that reinforce this philosophy.

Removing the dead wall

The dead wall consists of several stacks at the end of the wall, usually six to eight stacks or twelve to eighteen tiles, reserved for replacement draws after kongs or flowers rather than ordinary draws. Once the live wall is exhausted, the hand is drawn without using those reserved tiles.

A Historical Perspective on Zung Jung Mahjong devotes a chapter to this subject. The dead wall is a classical inheritance that preserves uncertainty and gives players defensive opportunities. But removing it also has a strong rationale: it reduces luck by making otherwise inaccessible winning tiles available, increasing wins and reducing draws. Both retaining and removing it have defensible arguments.

Chinese regional rules generally seek higher winning rates; many even remove honor tiles altogether. Retaining another dozen or more inaccessible tiles would reduce the usable supply further. Removing the dead wall has therefore become almost a consensus in Chinese Official and regional mahjong, and rules retaining it are now uncommon in China.

Removing winning prohibitions

The “passing-water” rule, also called a same-turn winning prohibition, means that after a ready player misses or declines a winning discard—or declines a self-draw—they cannot win on the same tile during that turn cycle, until drawing or taking a tile through a call.

The original purpose of prohibiting a win on an immediately repeated discard was to protect the player following suit, not to punish the player who missed a win. It seems unreasonable to pass one player's tile and win on an identical tile from the next player. Allowing this could facilitate targeting a particular player and provoke disputes about fairness. The restriction therefore gives the following player a safe discard. Once the cycle ends and the hand changes, the protection ends as well.

Japanese discard furiten is much stricter: a previously discarded tile cannot be claimed for a win, and merely including it among the current waits triggers furiten. A same-turn prohibition protects the following player without unduly restricting the winner and is therefore more reasonable than discard furiten.

Chinese Official Mahjong goes further and removes all such prohibitions. Indeed, patterns such as Last Tile and Melded Hand make winning on a repeated discard a specific technique. The four-point Last Tile requires the winning tile to be the last copy, with the other three publicly visible in discards or exposed sets. To reach eight points, a player may need to discard a tile from an already completed structure, bringing the visible count to three, then claim the final copy when the next player follows with it in the same cycle. Similarly, a self-drawn tile may not produce eight points, so a player pursuing the six-point Melded Hand must discard it and wait for a discard win.

To accommodate these patterns, Chinese Official Mahjong must therefore allow passing and then winning on a repeated tile. Following another player's discard is no longer safe, and targeting a particular opponent becomes a permitted strategy.