SSiW uses the short form such as do’n i’n mwyn and do’n i ddim yn mwyn. My text book uses the long form such as oeddwn i. Can someone run through the various other short forms for you, we, them.
Also how do you answer a question in the affirmative or negative using the short form. For example my book goes with ‘oeddwn, roeddwn i…’ and ‘nag oeddwn, roeddwn i…’. What would be the short form equivalents for I, you, we, them if you were answering in this way?
I hope how I’m going to write this out will make sense!
Roeddwn i / Oeddwn i / Doeddwn i ddim = ro’n i / o’n i / do’n i ddim
Roeddet ti / Oeddet ti / Doeddet ti ddim = ro’t ti / o’t ti / do’t ti ddim
Roedd e/o/hi / Oedd e/o/hi /Doedd o/e/hi ddim = doesn’t shorten
Roedden ni / Oedden ni / Doedden ni ddim - Ro’n ni / O’n ni / Do’n ni ddim
Roeddech chi / Oeddech chi / Doeddech chi ddim = Ro’ch chi / O’ch chi / Do’ch chi ddim
Roedden nhw / Oedden nhw / Doedden nhw = Ro’n nhw / O’n nhw / Do’n nhw ddim
The answers are usually an echo of the form used in the question, so the affirmatives in the shortened forms would be the ones above beginning with R and the negatives would be the ones beginning with D
e.g. O’n nhw canu neithiwr? Ro’n / Do’n.
BUT! There is a very useful trick for answers in the past tense - you can use “Do” (affirmative) or “Naddo” (negative) for all of them! 
Thanks. I did wonder if I could just get away with do and naddo.
Any thoughts on how many people use the short form of roedd compared to the long forms these days? Will you get a mixture or do most people opt for short form? Also do they tend to teach long or short in traditional evening classes?
In natural speech you’ll nearly always get the short forms. And in many areas even these are simplified, with the three-way distinction between (for example) Ro’n i, O’n i? and Do’n i ddim levelled further - squillions of Welsh speakers say O’n i, O’n i? and O’n i ddim in all circumstances. So all these are perfectly good and natural in speaking:
O’n i yn y dre neithiwr I was in town last night
O’n i yn y dre neithiwr? Was I in town last night?
O’n i ddim yn y dre neithiwr I wasn’t in town last night
I would definitely recommend these. As for the ones with R-, well they seem more natural with the long forms than the short - Roeddech chi and Roedden nhw sound OK if a bit formal, while Ro’ch chi and Ro’n nhw sound slightly odd and a bit ‘learnery’ to many native speakers (though they would be too polite to say so!), for which I think they would be much more likely to say O’ch chi and O’n nhw.
That’s the only bit I would disagree with there.
The answers definitely don’t have any prefix, so it’s
O’n nhw’n canu neithiwr? O’n/ Nag o’n.
diolch Gareth
(Someone’s going to come along here shortly and say ‘Well down our way in Abergynolwyn we ALWAYS say Ro’ch chi and Ro’n nhw, and I can well remember my old Nain and Taid saying it all the time’ - and then my name will be mwd round here!!!)