My topic is Wittgenstein's critique of Phenomenal Foundationalism, which is usually abbreviated to "The Private Language Argument". The abbreviation is unfortunate because it suggests that there is a single compact argument to be found somewhere in the discussion that starts at Philosophical Investigations § 243.¹ The favourite candidate is, naturally, the argument presented at § 258: if there were no available connections between types of sensation and anything in the physical world, sensationlanguage would be impossible, because the words in its vocabulary would lack criteria of correct application.