Rendaku (連濁): Why 手 + 紙 Becomes てがみ, Not てかみ

When two words join into a compound, the first sound of the second word often becomes voiced: か→が, さ→ざ, た→だ, は→ば, etc. So かみ becomes がみ, ひ becomes び, そら becomes ぞら.

It is not random. It signals “these two words are now one.” Recognizing it helps you read compounds correctly and understand why a familiar word suddenly sounds different.

The most useful exception: rendaku is blocked if the second word already contains a voiced consonant (が, ざ, だ, ば…). This is known as Lyman's Law.

So 風 (かぜ) already has a voiced ぜ, and 春風 stays はるかぜ, not はるがぜ. One voiced sound per element is the limit.

Rendaku is mostly a native-Japanese (和語, wago) phenomenon. Compounds built from Sino-Japanese on-yomi readings, like 学校 (がっこう) or 会話 (かいわ), rarely rendaku the same way, since those compounds were borrowed as whole units from Chinese rather than assembled from two Japanese words that fuse together. Loanwords written in katakana, like アイスクリーム, do not rendaku at all.

This gives you a quick filter when you meet an unfamiliar compound: if both halves are native Japanese vocabulary, especially common everyday words like 紙, 空, or 人, rendaku is worth checking for. If the compound is clearly built from on-yomi (Chinese-derived) readings, assume it stays unvoiced unless you have specific evidence otherwise.