I certainly don't mean to knock nominal types. But I think structural types are more fundamental. A language would only need a single "newtype" or "nominal" keyword to create nominal types from structural types.

Why structural is more fundamental?

C#'s anonymous type shares some flexibility of structural type system even though it still a nominal type.

  > A language would only need a single "newtype" or "nominal" keyword to create nominal types from structural types.