Robert Harper says that dynamically typed languages are actually statically typed languages but with a single type - the unitype. This type is a union of all of the runtime types, and so contains all of their combined values. Because of this Harper says that statically typed languages are a superior superset of dynamically typed ones. In them one could use a union type to create this unitype, and program in it as if it were a dynamic language. But of course no one does this, as it would be crazy, and therefore statically typed languages must be better.