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Five-Block Theory

How to group tiles

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Why use five-block theory?

  • Provides an intuitive way to group tiles
  • Aids in discard judgement
  • Good starting point for tile efficiency

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Image: Riichi Mahjong Central

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Why use five-block theory?

  • Groups / group candidates are tiles that can become a set.
  • Head / head candidate are tiles that can become the pair.
  • Blocks can be a group candidate, head candidate or both.

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Breaking down the hand

  • We can break apart our hands into groups of tile close in number

Image: Uzaku tile efficiency

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What to discard?

Image: Riichi Book I

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Waits

  • The strength of a group / block is based on what tiles it can accept
  • Side-wait / Ryanmen (strongest)
  • Middle-wait / Kanchan (weaker)
  • Edge-wait / Penchan (weakest)
  • Pair-wait / Shabo

Image: Riichi Book I

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Runs of 3+

Image: Riichi Mahjong Central

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In the case of six blocks

Discard the weakest block

Image: Riichi Mahjong Central

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In the case of six blocks

Image: Riichi Mahjong Central

4-pin would be the optimal discard here to get down to 5 blocks

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In the case of six blocks (no weak groups)

Image: Riichi Mahjong Central

  • We keep chance for chinitsu (all same suit) and don’t want overlapping waits so we drop manzu.
  • Discard 78m for safety and more points

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In the case of six blocks

Image: Riichi Mahjong Central

Best discard would be to get rid of the 9-pin pair over the 3-sou or 5-man.

  • Chance for tanyao(all simples) and sanshoku (same sequence in all suits)
  • Discarding middle tiles, especially red 5 is dangerous.
  • Discarding the red 5 gives the hand a value of 2600 instead of a possible mangan or haneman.