When Henry VIII needed a Rabbi

(7) The mitzvah of yibbum is prior to the mitzvah of halitzah. [This was so] at first when they intended to carry out the mitzvah. But now that they do not intend to carry out the mitzvah, the [rabbis] have said: the mitzvah of halitzah takes priority over the mitzvah of yibbum.

(1) The mitzvah of yibum comes before the mitzvah of chalitzah. And if she does not want to do yibum with another one of his [her husband's] brothers, or with the eldest who wants to do yibum, but without a satisfactory claim, she is considered rebellious. There are those who say that the mitvah of chalitzah is more important. The Rem"a comments: She is not considered rebellious if she does not want to perform yibum. Nevertheless, we do not force him to do chalitzah, rather they try to trick him if they are able to, for example that they say to him: do chalitzah on the condition that she give you a maneh [a coin equal to 100 zuz] (Tur in the name of Rabeinu Tam and the Ros"h). Specifically, if they are not among those who force him to divorce her, like was explained earlier in siman 154). If the two of them want to do yibum, we do not allow them to unless it is known that they both have intention to fulfill the mitzvah (Tur in the name of Rabeinu Tam). Some say that if he has another wife, we force him and pressure him until he does chalitzah (Tur in the name of the Sma"g). There are those who say that even if he doesn't have another wife, if the intention isn't for a mitzvah, and she does not want to do yibum, and they are not able to trick him, they force him to do chalitzah. The custom like the first opinion, that we do not force chalitzah at all, even if we know that his intentions are for money (Maharim Padvoah siman 18). But we appease between them like the communal institutions, like explained below. All this is when he wanys to perform yibum, and it is possible to do yibum without worrying about it being forbidden. But if he says he wants to do neither yibum nor chalitzah, we force him (Beit Yoseif in the name of Rabeinu Tam). Specifically, when she came with a reasonable claim, like explained in siman 154 (Truma Hadeshen siman 220). However, if it is possible to make him make a mistake by saying to him, take a lot of money for the chalitzah, we make him make a mistake so we don’t need to force him (N”Y M”K). They should be careful so they don’t plant money in the hands of a third person, because then they cannot say to him: we were just kidding with you (Mordechai Perek Hacholeitz). See later on siman 169 seif 50).

As it is taught in a baraita: Abba Shaul says that one who consummates a levirate marriage with his yevama for the sake of her beauty, or for the sake of marital relations, or for the sake of another matter, e.g., he wishes to inherit her husband’s estate, it is considered as though he encountered a forbidden relation, and I am inclined to view the offspring born from such a union as a mamzer. Since the prohibition against engaging in relations with one’s brother’s wife is overridden only for the sake of fulfilling the mitzva of consummating the levirate marriage, when one does not have the intention to fulfill that mitzva, the baseline prohibition applies, and so any offspring from the union will be mamzerim. The Rabbis say: The Torah states: “Her brother-in-law will have intercourse with her” (Deuteronomy 25:5), which indicates that he should do so in any case, even if his intentions are not solely for the sake of fulfilling the mitzva.