In his theory of natural laws David Lewis rejects the authenticity of impossible worlds on the grounds that the contradiction contained within his modifier "in (the world) w" is tantamount to a contradiction in the whole theory, which seems unacceptable. At the same time, in philosophical discourse very often researchers use counterfactual situations and thought experiments with impossible events and objects. There is a need to apply the theory of worlds to genuine, concrete, but impossible worlds. One way to do this is to reject Lewis's classical negation on the grounds that it leads to problems of completeness and inconsistency inside the worlds. The proposed extension for impossibility is compatible with Lewis's extensional metaphysics, although it leads to some loss for description completeness in semantics.