[DFHippie]

In Welsh you use "do" to assent to things asserted about the past. "Wyt ti wedi bwyta?" [Have you eaten?] "Do." [Yes.] The negative is "naddo". If you ask a question with something other than the verb initial, the affirmative is "ie" and the negative "nage". Otherwise, it works like you say in Irish or as in an English wedding ceremony. "Do you take so-and-so to be your lawfully wedded spouse?" "I do."

[talideon]

The 'tó' and 'náthó' mentioned in the article are actually borrowings from Middle Welsh into Middle Irish, but they fell out of fashion again. Old Irish didn't have yes/no equivalents.

'Tá' (present tense independent form of the verb 'bí') and 'tó' aren't thought to be related.