 Joyce’s point is this: Suppose we have three credence functions, \(c\), \(m\), and \(c'\). And suppose that, to move from \(m\) to \(c'\) is just to move in the same direction and by the same amount as to move from \(c\) to \(m\), which is exactly what will be true if \(m\) is the equal mixture of \(c\) and \(c'\). Now suppose that \(m\) is at least as inaccurate as \(c\)—that is, the change from \(c\) to \(m\) does not “improve accuracy”. Then, Joyce claims, \(c'\) must be at least as inaccurate as \(m\)—that is, the change from \(m\) to \(c'\) also does not “improve accuracy”.