the prohibitions only applied voluntarily. Thus in several prominent cases in the Torah, the incest rules are ignored in favour of marriage to a close relative; Jacob is described as having married his first wife's sister. Secular views Some secular Biblical scholars have instead proposed that forbidding incest with a daughter was originally in the list, but was then accidentally left out from the copy on which modern versions of the text ultimately depend, due to a mistake by the scribe. Rabbinic views In the 4th century BCE, the Soferim (scribes) declared that there were relationships within which marriage is prohibited, in addition to those forbidden by the Bible. These additional relationships were termed seconds (Hebrew: sheniyyot), and included the wives of a man's: father's half-brother on their mother's side mother's half-brother on their father's side grandfather grandson. The classical rabbis prohibited marriage between a man and any of his seconds, on the basis that doing so would act as a safeguard against infringing the Biblical prohibitions; one Talmudic opinion even arguing that the inclusion of the grandfather's wife and of the grandson's wife, among the seconds, is based on the Biblical rule against a wife's granddaughter. There was however some debate as to which relationships, other than the four listed above, counted as seconds; the Talmudic scholars and Rabbinic scholars of the middle age, the Rishonim, variously included or excluded the following relationships from the seconds of a man: grandmother's sister paternal grandfather's sister paternal grandfather's brother's wife grandfather's mother wife's great-grandmother wife's great-granddaughter (including great-granddaughter) an uncle's grandson's wife The extent to which the forbidden relationships extend beyond the seconds is a matter of dispute, but all the Talmudic scholars agree that marriage to the wife of any male descendant, in the direct male line, was forbidden; some classical rabbis also included the wife of any male ancestor, in the direct male line, in this prohibition, as did all of the Jewish scholars of the Middle Ages. In the Jerusalem Talmud, some of the opinions even include all blood descendants and ancestors of the seconds in the prohibition. In relation to seconds related only by marriage, some proposed the general principle that it would be acceptable to marry anyone only related to a "second" by a further marriage; for example, a wife of a father-in-law (apart from the mother-in-law), or the stepson's daughter-in-law. However, Israel Lipschitz interpreted this