Shape Attack Points
This page describes various shapes in Go, illustrating how good shapes can be built up from previously made good shapes. In addition, the attack points of shapes are listed. Generally speaking, a shape attack point is an empty intersection near a group of stones that, when occupied by an opponent stone, restricts the potential for either connectivity or eye shape.
The shape's orientation on the board is inconsequential.
A stone by itself, not touching or connected to any other stone, can be considered good shape. Its attack points are a one-point jump away, labeled a through d.
Two stones connected only to each other is a good shape called an Iron Pillar, Iron Post, or Tetchu. Its attack points are labeled a through f.
Two stones one space apart is a good shape known as Ikken Tobi, the One-Space Jump, or the One-Point Jump. Its attack points are labeled a through h.
Two stones diagonally adjacent from each other is a good shape called a Kosumi. Its attack points are labeled a through d. The stones, as shown, are considered connected.
The relationship between the two stones as illustrated is known as the Knight's Move or Keima. Its attack points are labeled a and b. The attack points are at positions that can help with separating the stones into two distinct groups, which can lead to complicated situations.
This illustrated relationship is known as the Large Knight's Move or Ogeima. Its attack points are labeled a and b.
This relationship is known by the rather inventive name of Very Large Knight's Move or Daidai-geima. Its attack points are labeled a through d.
A two-space extension can be attacked at a or b.
Good shapes with three stones build on good shapes with two stones.
A one-space jump from an Iron Pillar can be attacked at a to prevent the good shape known as the Bamboo Joint.
A two-space jump from an Iron Pillar can be attacked at a. Without supporting stones in the immediate vicinity, no other local move can separate the Iron Pillar from the extended stone. Be aware that there are ladder relationships that come into play when attempting to separate the shape.
The Tiger's Mouth or Kaketsugi, has a key attack point at a. This attack point prevents the opponent from making a Ponnuki shape. Notice how this good shape is is built upon a Kosumi.
The Dog's Head or sake bottle shape can be attacked at a (or by symmetry, b). This shape builds upon a one-space jump or a Knight's Move. The aim of the attack points is to, eventually, spoil the shape by playing at z.
The Tower shape can be attacked at a. A move at a aims to push through at z or y, whichever the opponent does not protect.
The Bamboo Joint can be attacked at the points a through f. Notice how a and d prevent a shape similar to the Tiger's Mouth.
The Ponnuki is not easily attacked, although the points from a to h are similar to the attack points of a Kosumi.