 Tractarian objects are what any “imagined”—or, more accurately, conceivable—world has in common with the real world (2.022). Accordingly, they constitute the world’s “fixed form” (2.022–3). ‘Fixed’ because, unlike the world’s content, objects (existentially speaking) hold fast in the transition from world to world. ‘Form’ because they constitute what is shared by all the worlds. (On Wittgenstein’s conception of possibility, the notion of an “alien” Tractarian object — one which is merely possible — is not even intelligible). If the objects make up the world’s form, what makes up its content? The answer, I think, is the various obtaining atomic states of affairs. Distinct worlds differ with respect to content because they differ with respect to which possible states of affairs obtain in them. A complication arises becasue possible atomic states of affairs also have both form and content form and content. Their form is the manner of combination of their components, their content those components themselves (that is, their contained objects). It follows that substance — the totality of objects — is indeed, as Wittgenstein says, “both form and content” (2.024–5). It is at once both the form of the world and the content of possible states of affairs (These and further details of this interpretation of Wittgenstein’s conception of substance as the fixed or unchanging are provided in Proops 2004; see also Zalabardo 2015, Appendix II for more on simples, names, and necessary existents). 