Why did "bydd" not mutate? The Tips & notes for this section said that there is a soft mutation when used in a question or negative statement.
No mutation is necessary after the question words pryd?, ble?, pam?, sut? (how?). If the questions requires the third person ydy/ydyn/mae/maen it is mae/maen that is used. You often do hear some people mutate after them and using ydy/ydyn, but it is incorrect.
In simple direct questions following pwy?, pa?, faint?, beth?, sut? (what kind of?) the mutation is required (or ydy/sy/ydyn). (In some indirect questions using those words there should not be a mutation, but that is not really in the scope of a basic course.)
The question forms of verbs without the question words do mutate:
- Fydd e yno heno? - Will he be there tonight?, but...
- Pryd bydd e yno? - When will he be there?
Sut bydd e'n teithio? - How will he travel?
Bryniff hi gar? - WiIl she buy a car?, but...
- Pam pryniff hi gar? - Why is she buying a car?
- Sut mae hi'n gallu ei fforddio? - How can she afford it?