Hello Wilburn,
That is definitely a great question and yes there are rules even though exceptions always exist in linguistic way.
You could look up this video
:Intermediate Lesson #14 - Mind Your Own Business
This has the explanations on the grammatical changes on verb forms so it would give you some insights on that!
Please let us know if you do not understand well and would like to further ask!
We would like to answer for you anytime
Thank you
Madison
Team Koreanclass101.com