Writing a method in EIEIO is similar to writing a function. The differences are that there are some extra options and there can be multiple definitions under the same function symbol.
Where a method defines an implementation for a particular data type, a generic method accepts any argument, but contains no code. It is used to provide the dispatching to the defined methods. A generic method has no body, and is merely a symbol upon which methods are attached. It also provides the base documentation for what methods with that name do.