A woman in Majorca was engaged to a man from Aragon before the local inquisition (decades before the famous inquisition throughout Spain) and was unable to get married after the decree. A "Marrano" friend of the first man "married" her before a priest without the presence of Jews. They lived together as husband and wife for a few months and after she became pregnant, the man abandoned her. The woman wanted permission to remarry and the question was whether she needed a get considering that she did not have a Jewish wedding.
It is clear that the wedding ceremony run by the priest did not create kiddushin, even if there would have been kosher witnesses. This is because the priest’s ceremony does not include giving an object of value from the groom to the bride, but just the priest’s declaration that they are married. However, one has to consider whether the fact that they lived together, so that everyone knows that they had marital relations, can serve as kiddushin (based on Gittin 81a). In (see ibid.) certain cases, we say that the witnesses to a couple’s yichud (being together in a secluded place) are equivalent to witnesses of marital relations, which is a means of kiddushin (Kiddushin 2a).
However there are three reasons why we cannot assume kiddushin despite the fact that they had relations (she is pregnant) and people knew about it. One reason is that the fact that their used a priest to marry is a sign that they were not interested in having a halachic marriage, Under such circumstances, we do not employ the assumption that a couple does not want to live in sin, i.e., without valid kiddushin, if they can avoid it. Secondly, the woman was required to go to the mikveh prior to the wedding and after the inquisition decree she did not have a place to go. Thus, since either way they would be living in sin, there are insufficient grounds to say that they had intention for kiddushin to avoid sin. Finally, we cannot consider people who generally knew the couple was living together as witnesses of yichud. Only the Ra’ah considers this testimony, whereas according to everyone else, there need to be witnesses for a specific known yichud.
[This responsum of the Rivash is one of the most basic sources regarding the question of whether in modern times, a Jewish couple who are civilly married require a get after the dissolution of their union. Piskei Din Rabbaniim vol. XIII, pp.106-143 is one of many sources which discuss the Rivash’s opinion. While the logic of whether or not the couple is interested in a Jewish marriage may change from case to case, the most objective leniency for not requiring a get is the idea that the witnesses of yichud must be witnesses to yichud at a specific time and place. The dayanim point out that the Rama, Even Haezer 149:1 rules like the Ra’ah (with whom the Rivash argues) that even general knowledge by a part of the populace that the couple are generally living together as husband and wife suffices.]
261 - Returning an Owner’s Family Members
262 - Divorce After a Non-Halachic Wedding
263 - The Law of Bar Metzra