I think one needs to be clear about the difference between "typing" and "type-checking". Typing means that objects can be instances of one or more type. Type-ch

I think one needs to be clear about the difference between "typing" and "type-checking". Typing means that objects can be instances of one or more type. Type-checking means that we can annotate the code so that it contains assertions about the types of its objects. Static type declarations can help program understanding a lot without no effect on performance. But on the other dynamic assertions of properties of objects can be more flexible, you can program your own type-checking algorithms and define your own types and what it means to be a member of them.