There are two ways of saying could have in Welsh, using gallwn (south) and medrwn (north). It’s best to be aware of both, and let local usage dictate which one you use.
Use wedi , not yn . Verbnouns such as gweld , to see , and the negative particle dim do not take soft mutation after wedi . Medrwn is sometimes used with the affirmative particle mi which does cause soft mutation.
Affirmative
English Welsh Alternative Examples I could have medrwn i fod wedi mi fedrwn i fod wedi medrwn i fod wedi gweld you could have medret ti fod wedi mi fedret ti fod wedi medret ti fod wedi gweld he could have medrai fo fod wedi mi fedrai fo fod wedi medrai fo fod wedi gweld she could have medrai hi fod wedi mi fedrai hi fod wedi medrai hi fod wedi gweld Carys could have medrai Carys fod wedi mi fedrai Carys fod wedi medrai Carys fod wedi gweld the girls could have medrai’r merched fod wedi mi fedrai’r merched fod wedi medrai’r merched fod wedi gweld we could have medren ni fod wedi mi fedren ni fod wedi medren ni fod wedi gweld you could have medrech chi fod wedi mi fedrech chi fod wedi medrech chi fod wedi gweld they could have medren nhw fod wedi mi fedren nhw fod wedi medren nhw fod wedi gweld
Interrogative
English Welsh Alternative Examples could I have? fedrwn i fod wedi? – fedrwn i fod wedi gweld? could you have? fedret ti fod wedi? – fedret ti fod wedi gweld? could he have? fedrai fo fod wedi? – fedrai fo fod wedi gweld? could she have? fedrai hi fod wedi? – fedrai hi fod wedi gweld? could Carys have? fedrai Carys fod wedi? – fedrai Carys fod wedi gweld? could the girls have? fedrai’r merched fod wedi? – fedrai’r merched fod wedi gweld? could we have? fedren ni fod wedi? – fedren ni fod wedi gweld? could you have? fedrech chi fod wedi? – fedrech chi fod wedi gweld? could they have? fedren nhw fod wedi? – fedren nhw fod wedi gweld?
Negative
English Welsh Alternative Examples I could not have fedrwn i ddim bod wedi – fedrwn i ddim bod wedi gweld you could not have fedret ti ddim bod wedi – fedret ti ddim bod wedi gweld he could not have fedrai fo ddim bod wedi – fedrai fo ddim bod wedi gweld she could not have fedrai hi ddim bod wedi – fedrai hi ddim bod wedi gweld Carys could not have fedrai Carys ddim bod wedi – fedrai Carys ddim bod wedi gweld the girls could not have fedrai’r merched ddim bod wedi – fedrai’r merched ddim bod wedi gweld we could not have fedren ni ddim bod wedi – fedren ni ddim bod wedi gweld you could not have fedrech chi ddim bod wedi – fedrech chi ddim bod wedi gweld they could not have fedren nhw ddim bod wedi – fedren nhw ddim bod wedi gweld