Nigan

In Go, nigan refers to the state in which a group of stones has secured two separate eyes, making it immune to capture under normal rules. This is a cornerstone concept in life-and-death situations (tsumego) and fundamental to understanding group safety.

To be considered “alive,” a group must be able to form two eyes that the opponent cannot fill without violating the rules against self-capture (suicide). If a group has only one eye or false eyes, it remains vulnerable and can be killed by the opponent.

The ability to read ahead and determine whether a group can form two eyes—or prevent the opponent from doing so—is critical in both attack and defense. Players must weigh the value of invading territory against the risk of being sealed in without the potential for two eyes.

Learn more about the concept of two eyes from our video