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 Raavya 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-khatĥila, 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 Raavya and Raavan, who maintain that hasava is not necessary nowadays.
If one drinks one of the four cups without reclining, the poskim are divided over whether or not he must go back and drink it a second time. According to Shulĥan Arukh, he must indeed 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 Raavya and Raavan who maintain that nowadays, when even important people are not accustomed to reclining, one need not perform hasava on the Seder night (SA 472:7, MB 21 ad loc.).
Shulĥan Arukh’s ruling that one must drink any of the four cups again with hasava, and Rema’s similar ruling about only the second cup, are le-khatĥila. If drinking again is difficult, one may rely on what he drank without hasava and need not drink again.
Women should preferably 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.
. The principle is that when in doubt about a Torah commandment one must be stringent, but when in doubt about a rabbinic enactment one may be lenient. Eating a kezayit of matza is a Torah obligation, and although reclining while eating is a rabbinic obligation, since it pertains to a Torah obligation we are stringent, and if one ate without reclining he must eat again and recline. Conversely, eating korekh and afikoman are rabbinic injunctions, and since according to Raavya and Raavan reclining while eating them is unnecessary, if one ate them without reclining, he would not have to eat again. However, since according to the overwhelming majority of poskim reclining is necessary when eating korekh and afikoman (and this is the halakha), and since it is an easy mitzva to redo, one should redo the mitzva.
Regarding korekh, Rokei’aĥ and Shibolei Ha-leket maintain that one need not recline while eating korekh since it contains maror. Manhig, though, says one should recline during korekh, and this is the view of most Rishonim as well as SA 475:1. However, if one ate korekh without reclining he still fulfills his obligation (Kaf Ha-ĥayim 475:36 in the name of Pri Ĥadash and SAH).
Regarding the afikoman, SA 477:1 states that one must recline while eating the afikoman. Pri Ĥadash, on the other hand, notes that Rambam and the Yerushalmi seem to 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-ĥayim 472:45 and 477:7. According to Ĥayei 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 Ĥag Be-ĥag 22:5.
. Pesaĥim 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 Halawa, 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. According to this answer, if one drank the cups without reclining, he need not drink again, since, in principle, the Gemara would have ruled leniently were this not such an easy mitzva. 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 Raavya and Raavan maintain that there is no need to recline nowadays, and we are uncertain about whether or not one is required to drink again, one may be lenient. This is the opinion of Birkei Yosef 472:8 and Kaf Ha-ĥayim 472:42. Ĥazon 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 preferably follow SA that if one drank any of the cups without reclining, he has to drink again, and 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.
. Pesaĥim 108a states that a woman need not recline if she is in her husband’s presence, with the exception of an important woman (“isha ĥashuva”). 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 ĥashuva – 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 ĥashuvot, but the custom is nevertheless that they do not recline, as per Raavya, who says 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-ĥayim (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 ĥashuvot or because the view of Raavya 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 Raavya.