The psychoanalyst, Anna Freud, famously said: “A mother's job is to be left” (and I'm sure she'd say the same for father's)! In today's hectic world, though, many moms and dads don't set such far-ranging parenting goals. Instead, they just try to get through each day and handle problems with their kids as they come.
If, however, your ultimate aim is to rear a child who will become a competent, independent, and contributing adult member of society, you want to use a combination of logical and natural consequences. Natural consequences are far more age-appropriate for young adults.
Logical consequences are stated in advance by the parents, understood by the child, and are related to the unwanted behavior. A dad, for example, may tell his teenage son that he can borrow the car but only if he returns it with a full tank. He makes it clear that, if that doesn't happen, the penalty will be no use of the car for a week.
Natural consequences, on the other hand, are what parents should rely on as their kids grow older instead of creating consequences for them. Unfortunately, many moms and dads are too anxious to let their kids fail. Therefore, they make the mistake of sheltering them from natural consequences.
A mom, for instance, has bribed her daughter in the past to study for her Spanish tests and has grounded her when she received a low score. Now, she's decided to take a step back and rely on natural consequences, realizing her daughter needs to experience the full negative impact of failing to study. She doesn't let her fears overpower her better judgment, deciding her daughter must contend with the natural consequences, whether that means getting a low grade, having to repeat the class, or not going to college. Most parenting experts agree that natural consequences are far and away the most effective way for kids to learn.
If by “young adult,” you mean your child is of legal age, it may be time to accept that your parenting responsibilities are over now. Your adult child's defiance may be signaling that it's time for them to make their way in the world. If they're not abiding by the agreements you've made, it would be reasonable to give them three months notice to find another living arrangement. This would not be a punishment or a rejection but a realization that they need to take the reins of their life. At this point, your involvement may be hindering their journey into adulthood rather than helping it. I wish you well with that.