[midhir]

"So we can look at, for example, Old Irish, where they said tó to mean yes"

Really? In modern Irish we substitute Tá for yes but it's not really yes. We don't have yes or no, we repeat the verb of the question positively or negatively. Tá is kind of 'am', níl 'am not' like

"Are you going to watch Mrs Browns Boys tonight?" "I am not."

Are they really comparable? Maybe somewhere along the line Tá (pronounced 'taw') was taken for 'yes'.

[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.

[danaliv]

I was wondering about this. Thanks for chiming in. I don't know Irish but I do know a bit of Scottish Gaelic, and it is as you say: there is no word for yes (or no), not even in the way the author suggests. Affirmation or negation is done by repeating the verb of the question. In the case of simple "to be" questions, that verb is either tha or 's. But a question like "have you read the book?", which would be structured "read you the book?", would be answered either "read" for the affirmative or "(not) read" for the negative.

In any event, tha—which I presume is the Scottish equivalent to Irish tá—doesn't mean yes either.

[talideon]

That's not quite right. 'Tá' only means 'yes' when answering a question in the present tense that uses the verb 'bí', e.g., 'An bhfuil tú anseo? Tá.' ('Are you there? (I) am' - 'bhfuil' is from the dependent form of the verb 'bí').

OIr 'tó' and 'tá' aren't (directly at least) related. From what I can dig up from eDIL, 'tó' and 'náthó' are borrowings of the Welsh 'do' and 'nado' that later fell out of use again.

[euccastro]

Echoing back the verb is a common way to reply affirmatively in Portuguese and (traditional) Galician. I hear that was common in Latin too. For some old Galician people, replying "yes" to a question is comprehensible but a mark of rudeness.

[jodrellblank]

"Are you hungry?" "I am and I amn't".

"Will you run away with yourself" "I willn't!"