2.0141 The possibility of its occurrence in states of affairs is the form of an object.

So circumstances [states of things?] are states of affairs after all, presumably. Otherwise this is a definition of the form of an object. Black (p. 55) says it is such a definition.

Black (p. 38): “Later on, we shall learn that form is the possibility of structure (2.033): every remark about ‘form’ can be made to yield a remark about ‘possibility’ and conversely. It is very difficult to advance beyond this point and to form a distinct idea of what Wittgenstein intends by either word.”