If the following prepositions are used as they are, without an ending, they will cause a soft mutation. The following prepositions cause a soft mutation when followed by a noun:

• am
• ar
• at
• heb
• i
• o
• dan
• dros
• drwy
• gan
• wrth
• hyd

e.g.

gwrando ar raglen radio

talu am ddau docyn

mynd i gael swper cynnar.