Here's a breakdown:
* "-ance" is used when the related verb ends in "-ant" or "-ancy". For example:
* "important" --> "importance"
* "constant" --> "constancy"
* "distant" --> "distance"
* "-ence" is used when the related verb ends in "-ent" or "-ency". For example:
* "independent" --> "independence"
* "violent" --> "violence"
* "confident" --> "confidence"
Let me know if you have any other questions!