Yotsugana

Yotsugana (四つ仮名^?, literally "four kana") are a set of four specific kana, じ, ぢ, ず, づ (in the Nihon-shiki romanization system: zi, di, zu, du), used in the Japanese writing system. They historically represented four distinct voiced morae (syllables) in the Japanese language; however, today, in standard Japanese and the dialects of most Japanese speakers these morae have merged down to two sounds.

Most of the far northern dialects (Tōhoku dialects and Hokkaidō) and far southern dialects (notably Okinawan Japanese) and the Ryukyuan languages (the other Japonic languages) have also mostly merged these down to one sound. However a few dialects, namely around Shikoku and Kyushu in the southwest, have conserved the distinction between three or all four sounds.

In the current Tokyo dialect, on which the modern standard Japanese language is based, and also in the widely spoken Kansai dialect, only two sounds are distinguished, as represented in the Hepburn (ji, ji, zu, zu) and Kunrei (zi, zi, zu, zu) romanization systems.

The spelling differences between the four kana were retained well up to the mid-twentieth century, long after the different sounds they represented had merged. That left two distinct morae in most mainland dialects, such as that of Tokyo.

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