>#3 and #4 defeat OOP

Again, it all depends. #4 might be entirely appropriate if there was no common interface needed among the classes; i.e. if there was no need to treat Vehicles polymorphically. In the VFP world, we don't descend all classes from a common base class, like they do in Smalltalk.

#3 might well be the best solution, if the concept of moving doesn't need to be treated polymorophically. The concept of "moving" might be too general for a given app.