Tagai-sen

Tagaisen, literally “alternate first,” is a Japanese Go term used to describe a format of play in which both players take turns playing Black in consecutive games, reflecting an equal match without handicap. Historically, this format predates the widespread adoption of komi and was used in professional match series where parity in skill was assumed.

In pre-komi Go, tagaisen meant that players alternated the first move without compensation. When one player achieved a certain lead—often three wins—the match format shifted to sen-ai-sen, giving the stronger player White in every third game. The decisive game in such shifts was called a kadoban.

With the introduction of komi in the late 1940s, tagaisen evolved to describe games played with standard komi under equal conditions—what is now considered the default format for most even games.