  For such cases, Aristotle shifts from a formal to a semantically based criterion of opposition (17b16–25). Members of an A/O pair (“Every man is white”/“Not every man is white”) or I/E pair (“Some man is white”/“No man is white”) are contradictories because in any state of affairs one member of each pair must be true and the other false. Members of an A/E pair—“Every man is just”/“No man is just”—constitute contraries, since these cannot both be true simultaneously but can both be false. The contradictories of these contraries (“Not every man is just”/“Some man is just”) can be simultaneously true with reference to the same subject (17b23–25). This last opposition of I and O statements, later to be dubbed subcontraries because they appear below the contraries on the traditional square, is a peculiar opposition indeed; Aristotle elsewhere (Prior Analytics 63b21–30) sees I and O as “only verbally opposed”, given the consistency of the I statement, e.g. “Some Greeks are bald”, with the corresponding O statement, “Some Greeks aren't bald” (or “Not all Greeks are bald”, which doesn't necessarily amount to the same thing, given existential import; see traditional square of opposition). 