Rock-paper-scissors (sometimes called ‘roshambo’) is a zero-sum hand game usually played between two people, in which each player simultaneously forms one of three shapes with an outstretched hand. These shapes are ‘rock’ (fist), ‘paper’ (flat palm), and ‘scissors’ (a fist with the index and middle fingers together forming a V). Each beats one of the other two, and loses to the other (i.e. ‘paper covers rock, but ‘scissors cut paper,’ and ‘rock crushes scissors’).
The players usually count aloud to three, or speak the name of the game (e.g. ‘Rock Paper Scissors!’ or ‘Ro Sham Bo!’), each time either raising one hand in a fist and swinging it down on the count or holding it behind. They then ‘throw’ by extending it towards their opponent. If both players choose the same shape, the game is tied and is usually immediately replayed. The game is often used as a choosing method in a way similar to coin flipping, drawing straws, or throwing dice. Unlike truly random selection methods, however, rock-paper-scissors can be played with a degree of skill by exploiting non-random behavior in opponents.
There are a number of more elaborate deadlock games. As long as the number of moves is an odd number and each move defeats exactly half of the other moves while being defeated by the other half, any combination of moves will function as a game. For example, 5-, 7-, 9-, 11-, 15-, 25-, and 101-weapon versions exist. Adding new gestures has the effect of reducing the odds of a tie, while increasing the complexity of the game. One popular five-weapon expansion is ‘rock-paper-scissors-Spock-lizard,’ invented by Sam Kass and Karen Bryla. ‘Spock”‘ is signified with the ‘Star Trek’ Vulcan salute, while ‘lizard’ is shown by forming the hand into a sock-puppet-like mouth. Spock smashes scissors and vaporizes rock; he is poisoned by lizard and disproven by paper. Lizard poisons Spock and eats paper; it is crushed by rock and decapitated by scissors.
In many real-time strategy, first-person shooter, and role-playing video games, it is common for a group of possible weapons or unit types to interact in a rock-paper-scissors style, where each selection is strong against a particular choice, but weak against another, emulating the cycles in real world warfare (such as cavalry being strong against archers, archers being strong against pikemen, and pikemen being strong against cavalry). Such game mechanics can make a game somewhat self-balancing, and prevent gameplay from being overwhelmed by a single dominant strategy. Many card-based video games in Japan use the rock-paper-scissors system as their core fighting system, with the winner of each round being able to carry out their designated attack. Other games use simple variants of rock-paper-scissors as subgames.
The first known mention of the game was in a 15th century book, ‘Wuzazu,’ by the Chinese Ming-dynasty writer Xie Zhaozhi, who wrote that the game dated back to the time of the Chinese Han dynasty (206 BCE). In the book, the game was called ‘shoushiling’ (lit: ‘hand command’). Throughout Japanese history there are frequent references to ‘sansukumi-ken’ (‘fist games with a three-way deadlock’). The earliest Japanese ‘sansukumi-ken’ game was known as ‘mushi-ken,’ which was imported directly from China. In the game the ‘frog” (represented by the thumb) is superseded by the ‘slug’ (represented by the little finger), which, in turn is superseded by the ‘snake’ (represented by the index finger), which is superseded by the ‘frog.’ Although this game was imported from China the Japanese version differs in the animals represented. In adopting the game, the original Chinese characters for the ‘poisonous centipede’ were apparently confused with the characters for the ‘slug.’
The most popular sansukumi-ken game in Japan was ‘kitsune-ken.’ In the game, a supernatural fox called a kitsune defeats the village head, the village head defeats the hunter, and the hunter defeats the fox. Kitsune-ken, unlike mushi-ken or rock-paper-scissors, is played by making gestures with both hands. Today, the best-known ‘sansukumi-ken’ is called ‘jan-ken,’ which is a variation of the Chinese games introduced in the 17th century. The game uses the rock, paper, and scissors signs and is the game that the modern version of rock-paper-scissors derives from directly. Hand-games using gestures to represent the three conflicting elements of rock, paper, and scissors have been most common since the modern version of the game was created in the late 19th century, between the Edo and Meiji periods.
The ‘Paper Scissors Stone Club’ was founded in London in 1842. The charter appeared in Edition 1, Volume 1, of the club’s publication, ‘The Stone Scissors Paper.’ It read,’The club is dedicated to the exploration and dissemination of knowledge regarding the game of Paper Scissors Stone and providing a safe legal environment for the playing of said game.’ In 1918, the club’s name was changed to ‘World RPS Club.’ Soon after that, the club moved its headquarters to Toronto, Canada. In 1925, the club had more than 10,000 active members, changed its name the ‘World RPS Society,’ and hosted its first annual championship.
It is impossible to gain an advantage over a truly random opponent. However, by exploiting the weaknesses of nonrandom opponents, it is possible to gain a significant advantage. Indeed, human players tend to be nonrandom. As such, there have been programming competitions for algorithms that play rock-paper-scissors. In tournament play, some players employ tactics to confuse or trick the other player into making an illegal move, resulting in a loss. One such tactic is to shout the name of one move before throwing another, in order to misdirect and confuse their opponent. During tournaments, players often prepare their sequence of three gestures prior to the tournament’s commencement.
The strongest strategy employed by rocks-paper-scissor algorithms is history matching: searching for a sequence in the past that matches the last few moves in order to predict the next move. In frequency analysis, the program simply identifies the most frequently played move. Researchers at the University of Tokyo have created a robot hand that has a 100% winning rate playing rock-paper-scissors. Using a high-speed camera, the robot recognizes within one millisecond which shape the human hand is making, then produces the corresponding winning shape.
In 2006, American federal judge Gregory Presnell from the Middle District of Florida ordered opposing sides in a lengthy court case to settle a trivial (but lengthily debated) point over the appropriate place for a deposition using the game of rock-paper-scissors. The ruling in ‘Avista Management v. Wausau Underwriters’ stated: ‘Upon consideration of the Motion – the latest in a series of Gordian knots that the parties have been unable to untangle without enlisting the assistance of the federal courts – it is ORDERED that said Motion is DENIED. Instead, the Court will fashion a new form of alternative dispute resolution, to wit: at 4:00 P.M. on Friday, June 30, 2006, counsel shall convene at a neutral site agreeable to both parties. If counsel cannot agree on a neutral site, they shall meet on the front steps of the Sam M. Gibbons U.S. Courthouse, 801 North Florida Ave., Tampa, Florida 33602. Each lawyer shall be entitled to be accompanied by one paralegal who shall act as an attendant and witness. At that time and location, counsel shall engage in one (1) game of “rock, paper, scissors.” The winner of this engagement shall be entitled to select the location for the 30(b)(6) deposition to be held somewhere in Hillsborough County during the period July 11–12, 2006.’ The public release of this judicial order, widely circulated among area lawyers, was seemingly intended to shame the respective law firms regarding their litigation conduct by settling the dispute in a farcical manner.
In 2005, when Takashi Hashiyama, CEO of Japanese television equipment manufacturer Maspro Denkoh, decided to auction off the collection of Impressionist paintings owned by his corporation, including works by Cézanne, Picasso, and van Gogh, he contacted two leading auction houses, Christie’s International and Sotheby’s Holdings, seeking their proposals on how they would bring the collection to the market as well as how they would maximize the profits from the sale. Both firms made elaborate proposals, but neither was persuasive enough to get Hashiyama’s business. Unwilling to split up the collection into separate auctions, Hashiyama asked the firms to decide between themselves who would hold the auction, which included Cézanne’s Large Trees Under the Jas de Bouffan, worth $12–16 million.
The houses were unable to reach a decision. Hashiyama told the two firms to play rock-paper-scissors to decide who would get the rights to the auction, explaining that ‘it probably looks strange to others, but I believe this is the best way to decide between two things which are equally good.’ The auction houses had a weekend to come up with a choice of move. Christie’s went to the 11-year-old twin daughters of the international director of Christie’s Impressionist and Modern Art Department Nicholas Maclean, who suggested ‘scissors’ because ‘Everybody expects you to choose ‘rock.” Sotheby’s said that they treated it as a game of chance and had no particular strategy for the game, but went with ‘paper.’ Christie’s won the match and sold the $20 million collection, with millions of dollars of commission for the auction house.