Josen

Josen was a historical ranking and handicap system used in professional and competitive Go. In this format, one player—typically the stronger one—would always play White, while the opponent took Black. Unlike traditional handicap games, where multiple stones are placed at the start, josen balanced skill levels more subtly by consistently giving one player the first-move advantage throughout a series of games.

If the weaker player consistently won as White, the match format could progress to sen-ai-sen, where the players alternated taking Black, or even to an even game, tagaisen, reflecting an improvement in the weaker player’s skill.

Josen was widely used during the Edo period, particularly in matches between players from different Go houses. It remained relevant in professional settings until the adoption of komi-based ranking systems, which made even games the standard.

Today, josen is rarely used in modern tournament play but is still studied in historical Go records.