Third Line  

On a 19 by 19 board, it is thought the third line is easiest to earn territory on. It builds a fair amount of it and cannot be invaded anymore.

In this diagram, Black has about 12 points of territory along the left side.

Fourth line  

When Black plays here, he's has not built complete territory yet. His formation is still open to invasions.

The Fourth Line is the line of influence

Fourth Line  

When we play along the fourth line, it mostly has a different purpose than making territory. In this common joseki for example, White plays on the fourth line.

is not a move which creates territory. faces the center and not the side. faces the side, so we expect to earn the territory along the side.

Fourth Line - The Joseki continues  

Black "walks" along the third line, as Kageyama would say, with White "walking" along the fourth. Black earns the side territory, and white gets influence in the center. (the standard push at a by Black has been omitted for simplicity).

Such central influence can be used to build a moyo, to be combined into overall thickness, to attack or to invade elsewhere and use these stones as support.

Approaches and pincers

Approach and pincer  

is a low approach. is a high pincer. The issue of pincers is discussed at High vs Low Pincer.

See also

• High and fourth line
• Low and third line
• Influence
• Territory