In terms of logic, suppose a manuscript of the fifth century has one reading, but a manuscript of the eighth century has a different one. Is the reading found in the fifth-century manuscript necessarily the older form of the text? No, not necessarily. What if the fifth-century manuscript had been produced from a copy of the fourth century, but the eighth-century manuscript had been produced from one of the third century? In that case, the eighth-century manuscript would preserve the older reading.
