 In some cases, the strengthened or neg-raised contrary reading may become salient enough over time to block the literal interpretation, as when French Il ne faut pas partir—literally = “one needn’t leave” (an O vertex modal)—is now generally used only to express the stronger proposition that one must not-leave (E vertex). This is a modal instance of the general phenomenon of O \(&gt;\) E drift (Horn 1989), an upward shift along the right (negative) vertical of the modal square of opposition. Such squares were constructed by Cajetan, based on Aristotle’s De Interpretatione 21b10ff. and Prior Analytics 32a18–28 (see Oesterle 1962), and by other medieval commentators.