 But this “quirk” has deep roots, dating back to St. Anselm’s 12th century Lambeth fragments (Henry 1967, 193–94; Hopkins 1972, 231–32; Horn 1989, §5.2). Anselm points out that “non…omnis qui facit quod non debet peccat, si proprie consideretur”—not everyone who does what he non debet (“not-should”) sins, if the matter is considered strictly (with the contradictory reading of negation as the syntax suggests). The problem is that non debere peccare is standardly used to convey the contrary meaning debere non peccare rather than the literal contradictory (“it is not a duty to sin”). It is hard to stipulate e.g., non debet ducere uxorem (= “a man is free not to marry”) without seeming to commit oneself to the stronger debet non ducere uxorem, an injunction to celibacy (Henry 1967, 193ff.; Horn 1978, 200).