The doctrine of Middle Knowledge presupposes that conditionals of freedom (statements of the form ‘If A were circumstances C, he would perform X’) can be true. Such conditions are, where true, not true in virtue of the truth of any categorical proposition. Nor can their truth be modelled in terms of comparative similarity of possible worlds, because the structure of possible worlds is a necessary one, whereas the connection between antecedent and consequent of a conditional of freedom is a contingent one. Lewis and Stalmaker are committed to ‘conditional fatalism’, the view that things only would go a certain way if they would have to go that way. Although commitment to conditional fatalism does not itself import a commitment to fatalism, it is hard to find a separate motivation for it.