Stephen Mulhall presents a detailed critical commentary on sections 243-315 of Wittgenstein's Philosophical Investigations: the famous remarks on 'private language'. In so doing, he makes detailed use of Stanley Cavell's interpretations of these remarks; and relates disputes about how to interpret this aspect of Wittgenstein's later philosophy to a recent, highly influential controversy about how to interpret Wittgenstein's early text, the Tractatus Logico-Philosophicus, by drawing and testing out a distinction between resolute and substantial understandings of the related notions of grammar, nonsense and the imagination. The book is concerned throughout to elucidate Wittgenstein's philosophical method, and to establish the importance of the form or style of his writing to the proper application of this method.