Take one of the examples that I used: A teenager gets a couple of speeding tickets, and his parents decide that they are not comfortable letting him use the car.
This could be done in a punish-y way if the parents' goal is to make him feel bad so that he will remember the lesson. The point of taking away the car is to teach the kid a lesson, through a painful stimulus, and make it more likely that he will remember to drive slowly.
The parents haven't decided what they will do about their own behavior; they have decided what the kid will do.
The parents could take away the car in a non-punishy way, as well. They could decide that they do not feel comfortable letting the child drive without them, as he has proven that he won't be safe. But they are happy to drive with him because they want him to have practice driving carefully and have a chance to show them that they can trust him to be safe. They aren't trying to make him feel bad for his speeding by applying a negative stimulus; they are making a decision about what they feel comfortable doing, in the context of the kid's speeding. Instead of deciding what they will do to the kid, they are deciding what to do themselves with their own behavior.
The outcome of both of these situations is the same as regards the car. It's not being used right now by the kid. But as far as future learning is concerned, the situations are different. In the first one, the parents create an adversarial relationship with the child, letting him know that they will hurt him for his own good and that they will impose arbitrary time limits to punish him. They don't give him a way out, a way to earn back trust. He learns to hide his driving and car use from them, or he learns to do what they say and slow down because they say it.
In the second example, the parents show the kid they are on his team. Though they don't want him driving alone, they are willing to drive with him so that he has a chance to prove that he can slow down. The kid learns that, though his parents set a limit when they see danger for him, he can count on them to help him remove the need for the limit as soon as possible. They want him to enjoy driving, and they don't like to prevent something he enjoys; they just want him to do it safely.
I guess my main point is that "deciding what you will do" should focus on the parent's behavior, the behavior that he can control. When it becomes "decide what you will do to the kid to teach him a lesson," you've veered into the realm of punishment.
(A note for readers: I am not completely happy with this post, mostly because trying to identify exactly what is different about limit setting vs. punishment can be kind of hard. I know that punishment adds an extra bit of oomph on top of the limit setting. For info on this, read Jenn's post Discipline Without Punishment. What I am finding hard is understanding and expressing the difference in mindset between a parent deciding what he will do and a parent punishing. I'd love to hear your comments on this.)
