# English

In the compound verb 手伝う, we see the following sound change:

> て＋つ **た** う→てつ **だ** う

Unexpectedly, the た from つたう turns into だ. 連濁, at least with the 手+伝う
analysis, can't account for this, because it's not the first consonant of 伝う.

What happened here?

# Japanese

「手伝う」の発音についての質問です。

> て＋つ **た** う→てつ **だ** う

意外なことに、「つたう」の「た」が有声化されて「だ」になります。「手＋伝う」という解析であれば、「た」は「伝う」の最初の子音ではないので、連濁が原因にはならないと思います。

何が原因と考えられますか？
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2015-11-27T21:14:27.280
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etymology phonology rendaku
Why is the た in 手伝う voiced?
# English

There's two possible explanations here, and from a little bit of searching, it
doesn't seem like anyone knows which is right (or that anyone's really thought
much about it).

Option 1: Rendaku plus metathesis (as Earthling suggested). te + tsutau >
tedzutau > tetsudau. There might be another example of this happening with 舌鼓
- shita + tsutsumi > shitadzutsumi > shitatsudzumi (though for this one the
unmetathesised version seems to be valid in nonstandard dialects).

It's possible that this is a regular change restricted to words where the
second half is at least tVtVCV. It might just be irregular.

Option 2: 手伝う is not actually 手 + 伝う, but something else entirely; with the
kanji spelling the result of a folk etymology.

Those are the most likely possibilities.

# Japanese

有り得る説明は二つありそうです。少し調べてみたら、どちらが正しいか誰もよく分からないみたいです（そもそも誰もあんまり考えてないみたいです）。

一。 「不規則連濁」（連濁プラス音位転換、Earthlingさんの仮説）。て＋つたう → てづたう → てつだう。「舌鼓」はもう一つの例なのかもしれません
－ した＋つつみ → したづつみ → したつづみ （けど「したづつみ」という非音位転換した方も標準外の方言で可能みたいです）。

後半がtVtVCVの言葉に限られる規則的な音便の可能性がありますが、単に不規則の可能性もあります。

二。 「手伝う」という言葉は実は「手＋伝う」ではなくて、別の由来のある言葉だということ。その場合は漢字の由来は民間語源のはずです。

以上は最も有り得そうな可能性であるみたいです。
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I think this is not due to a shifted rendaku, but rather due to a change in
pitch accent that occurs in all compound verbs (つたう{LHH} → てつだう{LHHL}).

It’s difficult to say てつたう{LHHL} without the た sounding voiced, because the
‘a’ in た needs to be fully voiced to clearly pronounce the pitch drop, at
which point it sounds like the ‘t’ is voiced when you speak quickly enough.

Another example of this pronunciation phenomenon would be 恋い慕う. If you
pronounce it as こいしたう{LHHHL} it sounds like こいしだう, although the orthography
hasn’t changed to reflect that in the case of this word.
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