Question

How do I explicitly refer to the parameter as opposed to the member variable?

static recursive{

    public static List<string> output = new List<string>();

    public static void Recursive(List<string> output){
        ...
    }
}

Answer 1

An unqualified reference will always refer to the parameter because it is at a more local scope.

If you want to refer to the member variable, you need to qualify it with the name of the class (or this, for non-static member variables).

output = foo;              // refers to the parameter
recursive.output = foo;    // refers to a static member variable
this.output = foo;         // refers to a non-static member variable

But you should probably change the name anyway. It makes your code much easier to read.

And you shouldn’t have public static variables at all. All of the .NET coding style guidelines strongly recommend properties instead of exposing public fields. And since those are always camel-cased, this problem solves itself.