If one eats a kezayit of matza without reclining, he does not fulfill his obligation, as he has not performed the mitzva as the Sages ordained it, and he must eat another kezayit while reclining. Even if one has already recited Birkat Ha-mazon, he must wash his hands again, recite “ha-motzi,” and eat a second kezayit while reclining. In this case, however, one does not recite the “al akhilat matza” blessing a second time, because, according to Raavyah and Raavan, he already fulfilled the mitzva of eating matza with the kezayit he ate without hasava (SA 472:7, MB ad loc. 22).
If one forgets to recline for korekh, he need not eat it a second time, since some poskim rule that korekh does not require hasava because it contains maror. Le-khatḥila, we customarily recline for korekh, but if one forgets to do so, he may rely upon those who maintain that hasava is not necessary. If one eats the afikoman without reclining and he can easily eat another kezayit of afikoman while reclining, he should do so; but if eating another kezayit will be difficult for him, he may rely on Raavyah and Raavan, who maintain that hasava is not necessary nowadays.
If one drinks one of the four cups without reclining, the poskim are divided about what he must do. According to Shulḥan Arukh, he should le-khatḥila drink the cup again, this time reclining. According to Rema, though, this creates a problem, because by drinking again one appears to be adding to the number of cups ordained by the Sages. Therefore, if one drinks the second of the four cups without reclining, he must drink it again with hasava, because the second cup precedes the meal, and since it is permissible to drink wine during the meal, one who drinks at this point does not appear to be adding to the required four cups. But if one forgot to recline while drinking the first, third, or fourth cup, he may not go back and drink it a second time, because by doing so he would appear to be adding to the mitzva. He may rely on Raavyah and Raavan who maintain that nowadays one need not perform hasava on the Seder night (SA 472:7, MB 21 ad loc.).
Shulḥan Arukh’s ruling that one must go back and drink any of the four cups again with hasava, and Rema’s similar ruling about only the second cup, are le-khatḥila. If drinking again is difficult, one may rely on what he drank without hasava and need not drink again.
Le-khatḥila, women should recline while eating matza and drinking the four cups of wine, but if they forgot, they need not eat or drink again. Important women who accidentally eat matza without reclining should eat it again while reclining.
Regarding korekh, although the halakha s that one must recline, in accordance with the view of Manhig and most Rishonim (SA 475:1), since some maintain that it is not necessary to recline for korekh because it contains maror (Roke’aḥ, Shibolei Ha-leket), and some are uncertain (R. Yeḥiel, cited by Tur), if one did not recline, it is not necessary to go back and do it again (Pri Ḥadash, SAH, Kaf Ha-ḥayim 475:36).
Regarding the afikoman, SA 477:1 states that one must recline while eating the it. Pri Ḥadash, on the other hand, notes that Rambam and the Yerushalmi imply that reclining while eating the afikoman is unnecessary. Based on this, MB 477:4 states that if one forgot to recline and eating another kezayit of afikoman would be difficult for him, he need not eat another afikoman. This is also the opinion of Kaf Ha-ḥayim 472:45 and 477:7. According to Ḥayei Adam 130:13, though, even if one was able to eat another afikoman, it is forbidden to eat the afikoman twice. MB 472:22 quotes this, which seemingly contradicts what he states in 477:4. Perhaps this can be reconciled: if one remembered immediately that he neglected to recline, he should continue eating another kezayit while reclining, but if he already finished eating, he should not go back and eat more, since this would be considered eating the afikoman twice. So states Hilkhot Ḥag Be-ḥag 22:5.
. Pesaḥim 108a expresses uncertainty about which of the four cups require reclining – the first two or the last two – and concludes that one must recline while drinking all four cups. Some Rishonim ask why the Gemara rules stringently, to recline during all cups, if the mitzva to drink the four cups is only rabbinic in origin, which should indicate a lenient ruling. Maharam Ḥalawa, Tashbetz, and others answer that indeed the Gemara should have been lenient, but since there is no difficulty involved in reclining, it is best to recline while drinking all four cups. Their view implies that if one drank the cups without reclining, he need not drink again, since this is an uncertainty about a rabbinic enactment, and we thus rule leniently, and there is no need to drink the cup again. In contrast, Rosh says that if one drank any of the cups without reclining, he must drink again. This leads us to the conclusion that the reason we recline during all four cups is not because we are in doubt, but because the Sages in fact decreed that this should be so. This is the opinion of SA 742:7. In practice, since Raavyah and Raavan maintain that there is no need to recline nowadays, this introduces another uncertainty, and according to halakhic principles, in cases of uncertainty about rabbinic law, we are lenient. This is the opinion of Birkei Yosef 472:8 and Kaf Ha-ḥayim 472:42. Ḥazon Ovadia (§13), however, rules in accordance with SA that the leniency to not have to drink again only applies to someone who has difficulty doing so. In sum, Sephardim follow SA and re-drink any cups that one initially drank without reclining. Ashkenazim follow Rema and only re-drink the second cup. However, if someone, whether Sephardic or Ashkenazic, wishes to be lenient, he may do so, since this is an uncertainty – and possibly a double uncertainty (sfek sfeika) regarding a rabbinic law.
. Pesaḥim 108a states that a woman need not recline if she is in her husband’s presence, with the exception of an important woman (“isha ḥashuva”). SA 472:4 rules accordingly. (The rationale is that if reclining in the manner of free people does not reflect an inner sense of freedom, it has no purpose. This is similar to the logic behind a disciple not reclining in the presence of his rabbi.) There are different opinions about what defines an isha ḥashuva – that she is not subservient to her husband, that she is wealthy, that she is pedigreed, or that her husband does not mind if she reclines. Rema states that all women nowadays are considered ḥashuvot, but the common practice among women is nevertheless that they do not recline, based on the view of Raavyah that there is no longer a mitzva to recline. In practice, all women from all communities should try to recline, as Knesset Ha-gedola and Kaf Ha-ḥayim (ad loc. 28) state. Many Ashkenazic women in fact do so. But if a woman forgot to recline, she need not eat or drink again, since the mitzva of reclining is rabbinic, and there are several poskim who maintain that women are exempt, either because they are not ḥashuvot or because the view of Raavyah is correct. Nonetheless, it seems that women who see themselves as important should recline while eating the Torah-mandated kezayit of matza and refrain from relying on the opinion of Raavyah.