That's because there are two separate types of inheritance that often get conflated in popular OOP languages: subclassing (implementation inheritance) and subty

That's because there are two separate types of inheritance that often get conflated in popular OOP languages: subclassing (implementation inheritance) and subtyping (specification inheritance). The 'types' here are the interfaces in typical OOP languages, though their (especially Java) failure to orient types around them create much of the pain developers experience. See https://www.cs.utexas.edu/~wcook/papers/InheritanceSubtyping90/CookPOPL90.pdf https://www.cs.utexas.edu/~wcook/papers/InheritanceSubtyping...