Don't you get problems with equal Signatures but different meaning or different scale? Example:

interface SomethingWithAge{ age(); }

class Person{ age(); // age in years }

function classify( SomethingWithAge item ){ if( item.age() < 20 ){ print( 'young') } else{ print( 'old' ); } }

p = new Person( 33 ); classify( p ) // prints 'old'

class Message{ age(); // age in milliseconds }

c = new Message( 231443 );

classify( c ); // prints 'old'