The Sapir-Whorf hypothesis poses that our native language affects how we think. Computer programming languages also strongly affect how we think about, design, implement, and maintain code.
I was working on some tricky code this morning that builds on some Common Lisp CLOS class libraries. The new code is really orthogonal to the existing functionality and it seemed like a poor idea to merge the new in with the old, especially since the old codebase will probably be used as-is for a while. I decided to start a new module (as defined by physical file organization) that added the new functionality to the existing classes as generic methods. The new module stays small, and anyone needing to use the original codebase is not confused with extra code for functionality that they do not need.
In Ruby, I like to do the same sort of thing: have different modules (as defined by physical file organization) where new orthogonal functionality is added by defining new methods to existing classes in new file modules.
In Java (and other languages), you can always use Aspect-oriented programming (AOP) to add new orthogonal behavior to class libraries, but, to be honest, I dislike AOP - this is not the fault of AOP per se, but because I have only used AOP with Java.