"Basai'n well gyda fi adael nawr."
Translation:I would prefer to leave now.
Why is it sometimes 'fasai'n' and at other times 'basai'n'? I can't see an obvious reason
It is always "fasai'n" for questions and negatives, this is because there used to be a verbal particle that is now dropped. For positive statements you can either mutate or not mutate, there used to be a particle before this sentence too (Fe in the south and Mi in the north) which is now dropped (except it's pretty common to use Mi in the north), so since the particle is dropped it's up to you to decide if you want to mutate it or not.
Thanks - I knew about the changes depending on whether it was a positive or negative statement (and the change if it's a question) but didn't know that it was also optional in a positive statement, hence my confusion. Many thanks for a comprehensive answer.
The menu also shows 'It would be better for me to leave now'. In context, this is a reasonable sentence. But, despite the menu choices, only the translation at the top is being marked as correct.
Two different patterns and meanings:
- Basai'n well gyda fi.... - I would prefer...; I would rather...
- Basai'n well i fi... - I had better...; It would be better for me...
This is explained in the course notes - https://www.duolingo.com/skill/cy/Conditional/tips-and-notes/