Conflicts Between Kibud Av and Kibud Eim
The gemara in Kiddushin (31a) questions a situation where a child faces a conflict between his father's wishes and his mother's request. If each parent requests, for example, a glass of water, and the child can perform only one task, whose request should he fulfill? The gemara rules that his father's wishes should be addressed, since "the child and the mother are obligated to serve the father." Since the mother is beholden to perform domestic responsibilities for the father, the child should prioritize the respect owed to his father over the respect for his mother.
This halakha may be understood from two different standpoints. On the one hand, it might reflect a purely practical measure. By serving the mother, the food will inevitably be transferred to the father. Upon receiving a glass of water, the mother is obligated to yield it to the thirsty husband/father. To spare the unnecessary transfer, the water is immediately delivered to its final destination. A second manner of understanding would suggest that the gemara affords preference to the father for reasons beyond mere practical considerations. Inasmuch as the mother must also serve the father, kibud av is ranked as a 'higher' mitzva than kibud eim. Therefore, when presented with a conflict, a child should prioritize kibud av.
The difference between these two approaches would surface in a situation in which the mother is no longer obligated to serve a father. The simplest scenario would be a situation of divorced parents. In this case, since the mother is freed from her marital obligations, perhaps the child should no longer prioritize kibud av. If the gemara's ruling was based upon the practical consideration that ultimately the mother will surrender the water to the father anyway, in this instance such considerations would not apply. If, however, the gemara ruled categorically that kibud av is more stringent than kibud eim, these evaluations might apply even in situations when a mother is no longer obligated toward her ex-husband. This position is adopted by the Meiri, who rules that in such a scenario a person should endeavor to execute both mitzvot; if he cannot, then he should place the glass of water in front of the two of them without favoring one above the other. The Meiri brings a dissenting opinion which rules that even when the mother is no longer obligated to serve the father, the latter's wishes take precedence over the mother's. This position indicates that the gemara establishes a fundamental evaluation of kibud av as superior to kibud eim.
A second factor which might be impacted by our question involves a situation where both parents request of the child a service, that a woman is not obligated to perform for her husband. In this instance, we cannot prioritize the father on the basis of the practical consideration that the service will be rendered to the father by the mother ultimately. If halakha grants preference to the father even in such situations, it is presumably due to a fundamental decision that kibud av is superior because in general a mother is 'obligated' toward her husband. Therefore, even when this obligation is not expressed at a practical level, the father's wishes take precedence. This issue is mentioned by the Pitchei Teshuva (Yoreh Deah 240:9), who rules that in these situations the child does not give precedence to the father.
A third possible question is whether other factors can tilt the scale and grant precedence to a mother's wish. Presumably, if the prioritization of the father is merely practical, then no fundamental evaluation of the mitzva of kibud av has been rendered. Therefore, the practical consideration granting precedence to a father's wish might be overridden by competing concerns or interests. If, however, kibud av has been deemed more 'weighty' than kibud av, we might expect the preference to kibud av to be categorical, unsusceptible to conflicting considerations.
One such scenario is discussed by the Maharshal (Yam shel shlomo to Kiddushin), who rules that a mother is ransomed before a father, and, similarly, that an impoverished mother should be clothed prior to a father. In each of these instances, unique factors campaign in favor of assisting the mother before assisting the father. For example, a female hostage's situation is far more precarious than a male's, and it is certainly more humiliating for a woman to beg for clothing than it is for a male.
A second predicament is portrayed in a teshuva of the Noda Be-yehuda (Even Ha'ezer volume II teshuva 45). The teshuva describes a situation in which a father had issued a 'death-bed' order to his daughter not to marry a particular individual. Posthumously, the mother decided in favor of her daughter's marriage to that very man. Among the many halakhic issues brought to bear was the conflict between kibud av and kibud eim. A Rabbi named Rabbi Shmuel – a member of the Beit Din of Manheim - had ruled that the daughter might have to follow to deceased father's wishes. Even though (he assumed) a child of divorced parents may employ discretion in choosing between parental requests, the child of a deceased father must continue to prioritize his father. A divorced woman, this Rav claimed, is not obligated to honor her ex-husband, while a widow must continue to honor her husband. Since the widow is still obligated to honor her dead husband, the father's wishes still take precedence.
The Noda Be-yehuda responded in two-fold fashion. First, he disputed the basic assumption of this Rav that a widow must still honor her dead husband. The very fact that she is allowed to remarry suggests that she has been entirely released from her responsibilities toward her previous husband.
Having rebuffed this Dayan's first claim – a claim which would still prioritize the father's wishes above the mother's, the Noda Be-yehuda then invokes an entirely different argument. He writes that in this instance, the child has the responsibility to accede to the mother's wishes and not the father's since the former is alive while the latter is deceased. Even though, under normal conditions, kibud av takes precedence, when the mother is alive, she takes precedence. The Noda Be-yehuda probably understood the gemara's initial ruling as purely practical; as such, when other factors tilt the scale differently, the mother's wishes take precedence. Had he viewed the gemara's evaluation as fundamental, he might not have allowed alternate factors to grant priority to kibud eim.