What is Mentsu? Meaning, Types, and Building Methods Explained for Beginners

What is Mentsu (Set)?

Mentsu (面子) refers to a 3-tile combination in mahjong. A standard winning hand consists of “4 sets + 1 pair,” making sets the basic unit of hand building.

There are three types of sets: shuntsu (sequence), koutsu (triplet), and kantsu (quad), each with different combination methods.

Detailed Explanation of Mentsu

Types of Mentsu

Basic Winning Hand Structure

Standard winning hand: 4 sets + 1 pair

Example: 123-man 456-pin 789-sou east-east-east 55-sou
         └sequence┘ └sequence┘ └sequence┘ └triplet┘ └pair┘

Ease of Building Sets

1. Why sequences are easier to build

   • Easily become open waits
   • Easy to make with simples (2-8)
   • Many acceptance tiles

2. Why triplets are harder to build

   • Need to collect 3 identical tiles
   • Maximum of 4 tiles exists
   • Can’t make if opponents use them

Usage Examples

Real Game Situations

Example 1: Hand Structure Explanation

"One more set until tenpai"
"Too many sets (overflow), need to break one"

Example 2: Tactical Judgment

"Sequence-focused building seems faster"
"Have yakuhai pair, let's make it a triplet for 1 set"

Example 3: Calling Judgment

"Short on sets, let's call aggressively"
"Already have 3 sets, just need pair wait"

Basic Set Building Tactics

Efficient Set Building Methods

1. Prioritize ryanmen taatsu

   • 23, 45, 67 etc. are open waits
   • Most likely to become sets

2. Handling pairs

   • 3+ causes set overflow
   • Yakuhai worth making into triplets

3. Processing isolated tiles

   • Discard tiles unlikely to become sets early
   • Start with terminals (1, 9) and honors

5-Block Theory

Efficient hand building concept:

• 4 sets + 1 pair = 5 blocks is basic
• 6+ blocks is set overflow
• When 1 block short, consider calling

Related Terms

• Shuntsu: 3 consecutive numbered tiles
• Koutsu: 3 identical tiles
• Kantsu: 4 identical tiles
• Jantou: Pair in winning hand
• Taatsu: Incomplete set

Common Mistakes and Points to Note

Points Beginners Often Mistake

1. Miscounting sets

   • Kantsu also counts as 1 set
   • Distinguish closed/open triplets when scoring

2. Set overflow

   • Trying to make 5+ sets
   • Easily happens with too many pairs

3. Honor sequences

   • Cannot make sequences with honors
   • East-South-West-North, dragons are triplets only

4. Set shortage

   • Only completing 3 sets
   • Sometimes confused with chiitoitsu

Special Winning Hands

Forms Other Than 4 Sets + 1 Pair

Yaku Related to Sets

Yaku Determined by Set Types

• Toitoi: All triplets
• Sanankou: 3 concealed triplets
• Ikkitsuukan: Same suit 123, 456, 789
• Sanshoku doujun: Same numbered sequence in 3 suits

Conclusion

Sets are the fundamental building blocks of mahjong, and efficient set building is the first step to victory. Beginners should start with sequence-focused building, gradually learning to use triplets and quads as well. Keep the basic 4 sets + 1 pair structure firmly in mind and focus on efficient hand building.