Mentsu
Mentsu 「面子」, known as "tile groups", "melds", or "sets" in English, are used to form a standard winning hand. There are three types: shuntsu (sequences), koutsu (triplets; three-of-a-kind), and kantsu (quads; four-of-a-kind). Those types can be further split into "open" and "closed", and they can be composed of differing suits and tile numbers. There are also jantou (pairs), which are required for a standard winning hand, but are not tile groups.
A standard winning hand is composed of 4 tile groups + 1 pair. Therefore, forming tile groups is a central part of developing a mahjong hand; they are required to attain tenpai and win.
Rule overview
Each tile group must be composed of a single suit: for example, 123-pin is a valid sequence, but 12-pin + 3-sou is not. A hand can contain tile groups of different suits.
A group of honor tiles can only be composed of copies of that exact honor tile, meaning honors cannot be used in sequences.
Open vs closed
A tile group is open if it was completed by another player's discarded tile (completed by chii, pon, ron, or kan using a discard). Otherwise it is closed.
- Open tile groups cannot be changed once called.
- Open triplets and quads are worth half as much fu.
- The yaku of sanankou and suuankou count the number of closed triplets/quads.
Open/closed tile groups should not be confused with open/closed hands, as a closed hand can contain an open tile group. (This is because ron opens the tile group but not the hand.)
The tile groups
Shuntsu
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| Anjun - Closed | Minjun - Open | Minjun - Open (middle number called) |
Shuntsu 「順子」 ("sequences") are a tile group consisting of three consecutive number tiles. Note that 9 does not "wrap around" to 1 - you cannot have sequences of "891" or "912". In addition, you cannot make sequences by using honor tiles.
- Closed sequences are called anjun 「暗順」.
- Open sequences are minjun 「明順」. They can be formed with the call of chii. Open sequences can only be completed with the left player's (kamicha's) discard.
Koutsu
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| Ankou - Closed | Minkou - Open |
Koutsu 「刻子」 ("triplets") are a tile group consisting of three of the same type of tiles.
- Closed triplets are called ankou 「暗刻」.
- Open triplets are called minkou 「明刻」. They can be formed with the call of pon. Open triplets may be completed by using any player's discard.
Kantsu
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| Ankan - Closed | Daiminkan - Open | Shouminkan - Open (Added) |
Kantsu 「槓子」 ("quads") are special - in order for it to count as a proper tile group, a player must declare "kan". Kan is a special tile call with its own set of procedures: first, the four-of-a-kind must be set aside, then a player must draw a replacement tile.
- Closed kans are called ankan 「暗槓」, which can be formed by calling kan after drawing all 4 copies of a tile.
- Open kans may be collectively be called minkan 「明槓」, though there are two types:
- Daiminkan 「大明槓」 ("open kan") are formed by having a closed triplet, then calling kan on any player's discard.
- Shouminkan「小明槓」 ("added kan") are formed by having an open triplet, then drawing the 4th copy of a tile and calling kan.
Kantsu count as triplets for the purposes of yaku.
Jantou
Jantou 「雀」 is the pair of the hand. They are not considered "mentsu" or "tile groups", though a hand needs a pair to win.
External links
- Mentsu in Japanese Wikipedia