Reduction Is Worth As Much As An Invasion
The proverb Reduction is worth as much as an invasion addresses a common failing of untutored amateurs, which is to invade too often into the opponent's territorial framework (moyo). Instead, the option of reducing (Japanese keshi) the framework is advised or at least encouraged to be taken into account.
Caution: The proverb has no traceable source to an existing proverb in literature from those countries where professional Go is practiced.
A keshi play, or "erasure", is a move made on the edge of an opponent's framework (moyo) or just outside it. The idea is to allow him some territory, but not that much. Typical keshis are the shoulder hit, the cap (boshi) and a play on the border of a central moyo.
An erasing move is often the smart choice for several reasons:
- It is less risky than an invasion, especially when you don't have support in the area.
- While an invasion often permits the opponent to get outside thickness in exchange for losing some territory, a keshi move can help to build influence or contribute to a central moyo while keeping the opponent's area to manageable proportions. Look at it this way: if your keshi move reduces the enemy position by 7 points and gives you the chance to make central territory of about 8 points, then it is worth 15 points, which I'm sure you'll agree is not too shabby!
- Many keshi moves such as the shoulder hit and boshi have more severe potential follow-ups, should opportunity arise.
- Keshi plays are usually light and can help you to retain sente - although Fujisawa Hideyuki Sensei notes that you can expect to end in gote if you play the shoulder hit (see his book "Reducing Territorial Frameworks").
- Finally, it's often quite amazing just how much an enemy territory can be reduced by keshi.
Tamsin (2 kyu BGA)
Sometimes invasion is best, sometimes reduction. Just make sure not always to invade. (WME, see Bill Spight's statements in the discussion)
Keshi moves are more likely to be multi-purpose: Erasing moves on the edge of a moyo often help develop your own position while invasion moves create a weak group which must defend itself and are usually aimed just at destroying, not creating.