The Rabbinite and Karaite communities lived largely apart since the twelfth century. Although questions were raised as to the legal status of the Karaites, these discussions were mostly theoretical. The issues were whether or not the Karaites were to be considered Jews, and, if so, was it permissible to marry with them? The answer to the first question is surprisingly more complex than we might assume. We are generally raised on the concept that, no matter what one does, a Jew remains a Jew. As to an individual, this is certainly true. The idea is well established in the Talmud: "An Israelite, even if he sins, is still and Israelite". Nevertheless, the halachah requires a Jew who has apostatized to formally re-accept Judaism before a Beit Din, and to immerse. Essentially, this constitutes a mini-conversion.This,however, does not mean he wasn't Jewish until now. It is a way of showing public regret for his actions, as a prerequisite for community acceptance. That an unfulfilled Jewishness is nevertheless handed down for generations, as is generally assumed, really has no source. Yes, it is the view of most rabbis. But there was a significant minority of rabbis in the sixteenth century that believed that a family not identifying with the entire Torah, Written and Oral, ceased to be Jews after three generations. This view, however, is also without Biblical or Talmudic source. Another issue is their identity. The Karaites follow patrilineal descent. That is, the child of a Jewish father and a non-Jewish mother is regarded as a Jew.The understanding of traditional Judaism is exactly the opposite. So, how would we know if many generations back, any particular Karaite may have been the product of a marriage in which the matrilineal line line was not Jewish, rendering him a non-Jew? This was countered by many with the argument that Karaites did not intermarry. In fact, until the last few years, they did not accept converts! (and even now, it is the ersatz, online variety that have invented Karaite conversion)  The chance of a Karaite not having a Jewish matrilineal line would be exceedingly unlikely. Another issue was "mamzerut" (usually translated "bastardy"). Our understanding of this Biblical prohibition of marrying a Mamzer is understood by us to mean the progeny of an incestuous or adulterous union (the Karaites have a totally different understanding of the term). Now, Karaite divorce does not follow our understanding of the Biblical ceremony. Even if it did, it would still be invalid, as divorce, as well as many other rituals, requires two "kosher" witnesses. Karaites would be excluded, as their views and practices are seen as heretical, disqualifying them as witnesses. Therefore, all Karaites are under suspicion of being doubtful mamazerim. Many countered this argument with the idea that if their divorces lack kosher witnesses, so do their marriages! A child born out of wedlock is not a Mamzer. Therefore there is no reason to assume that any individual Karaite is under suspicion of being either not Jewish, or illegitimate Their views are seen as heretical, nonetheless. It would be virtually impossible to run a family under two theologies and two ideologies. The conclusion expressed in most classical sources is that if a Karaite renounces his (or his family's) ways, he is to be welcomed back into the community, and may marry whomever he pleases. There were, and are, dissenters to this approach, but it is the one widely accepted.
As I noted, these question were for centuries largely theoretical, as there was little mingling between the groups. This question became real and pressing as the two groups came to live together in modern Israel. It has been controversial for over seventy years, and remains so today. That will be my next post.