The thing is, the modern notion of what constitutes a type is 'class'. This stealthy switch from one to the other has made the concept of strong typing hard to

The thing is, the modern notion of what constitutes a type is 'class'. This stealthy switch from one to the other has made the concept of strong typing hard to understand and/or apply in practice, and with the addition of the idea of interfaces, late binding, etc. the problem of types in programming, stated in all its generality, became pretty much intractable.