A couple of weeks back, a co-worker was pondering a situation he was facing. He was looking at the following class hierarchy: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { } class FirstConcrete : SecondaryBase { } class SecondConcrete : SecondaryBase { } Basically, the first 2 classes are abstract classes, but the OriginalBase class has Test implemented as a virtual method. What he needed was to force concrete class implementations ......