Philosophical Investigations set the stage for debate about the possibility of a private language in 1953. Ever since then it has been at the centre of that debate. The evolution of the private language debate was, and still is, intimately tied up with developments in the interpretation of Philosophical Investigations. Wittgenstein’s thoughts have been so central to the debate that there is a sense in which most articles in previous chapters have served a dual purpose, illuminating both whether a private language is possible and why (and in what sense) Wittgenstein thought it was not. Clear as it might be that the interpretation of Wittgenstein is logically separate from the truth about private languages, the issues have been remained very close. By and large, developments and refinements in the private language argument have led to developments and refinements in our understanding of Wittgenstein. 1