Why does it make sense to give definition for a pure virtual function?

Question

Scott said on Effective C++, 3rd Edition, pg. 43 that to make an abstract class, we just need to give it a pure virtual destructor:

class AWOV {                      


        

Answer 1

By making a function pure virtual we force the user of the class to replace the function with another in the derived class.

The base class function can still be called with BaseClass::myfunction(...)

Now the base class might want to provide some core functionality that the derived class may use if it chooses to do so.