In this chapter, I interpret section 6.361 of Wittgenstein’s Tractatus – containing Wittgenstein’s second reference to Heinrich Hertz in the book – in the context of the nearby framing remarks concerning the ‘law of causality’. Attention to the relevant details of Hertz’s work sheds light on a number of Wittgenstein’s remarks about mechanics in the 6.3s and, in particular, explains Wittgenstein’s claim that ‘What can be described can happen too, and what the law of causality is meant to exclude cannot even be described’ (6.362). For Wittgenstein, to describe events in causal terms is to describe them via an appeal to temporal and spatial asymmetries. However, no alternative is available: a description that did not appeal to such asymmetries would not be a description of anything. According to the Tractatus, descriptions are recognized as causal when they are embedded in a unified theoretical framework, but causal powers, understood as relations of material necessity, do not exist.