The message "at:put:" is indeed a keyword that is part of the dictionary of the object and not just a generic dictionary. So each object has its own dictionary that associates keywords to method calls. So in Smalltalk you can not access neither variables (class or instance) nor methods (class or instance) outside the object, they all are accessed through messages. This happens to hide the implementation, hence the complexity of the object. The user does not need to know how the Object works only how to use it.