This paper distinguishes five key interpretations of the argument presented by Wittgenstein in Philosophical Investigations I, §258. I also argue that on none of these five interpretations is the argument cogent. The paper is primarily concerned with the most popular interpretation of the argument: that which that makes it rest upon the principle that one can be said to follow a rule only if there exists a 'useable criterion of successful performance' (Pears) or 'operational standard of correctness' (Glock) for its correct application. This principle, I suggest, is untrue. The private language argument upon which it rests therefore fails.