Effective method

An effective method for a class of problems is a method which, if followed rigorously, and as far as may be necessary, is logically bound to always give some answer rather than ever give no answer; always give the right answer and never give a wrong answer; always is completed in a finite number of steps, rather in than an infinite number; for all inputs, and for all problems of the class; for which each step in the method may be described as a mechanical operation.

Another sense of the term may include the qualification that when given a problem from outside the class for which the method is effective, the method may halt or loop forever without halting, but must not return a value as if it were the answer to the problem.