Why isn’t it important to lean while you are eating Karpas?
There is a dispute among the early authorities if leaning is required when eating karpas [between the Shibolei Haleket and Avudraham]. The accepted custom is with the opinion that leaning is not required. This debate seems to center around the nature of obligation to eat Karpas. Many Rishonim are of the opinion that in fact it’s purpose is merely to invoke the questioning of the children. As such it is not an obligatory eating which would require leaning, rather a “shinui” something different being done, and hence no leaning is required, which is only for obligatory eating of the night.
The first thing we do on Leil Haseder that makes this night different than all other nights is the טיבול ראשון, eating the כרפס. The source for this practice is the mishna in Pesachim [114a]. Rashi and the Rashbam both explain that the purpose of this dipping is to arouse the curiosity of the children, to ask about the difference of this night. This is an opening to begin to explain the significance of Leil Haseder.
Being that this is only to bring the children to ask, we can understand the opinion of many Rishonim that Karpas does not requires a Kzayis. Only Matza and Maror where there is a mitzvah to eat, do we require a kzayis, here the point is only to make a shinui. The opinion of the Rambam however is that in fact Karpas requires a complete kzayis. Although the Gemara does indicate that Karpas is so the children will ask, according to the Rambam, there is a mitzvah beyond that, similar to eating Maror. Perhaps the Kapras also serves as a זכר to the slavery and subjugation, and so a vegetable, slave food, is eaten. In fact the Rambam writes that the Karpas is also dipped in
This question on the Rambam from the Gemara is actually asked by Tosfos [115a s”v hadar]. Tosfos there brings another explanation for Karpas, in order to make a Borei Pri Hadama now, to cover the Maror later, so as not to need to make 2 berachos on the Maror, as this would violate the principle of אין עושין מצות חבילות חבילות [bunching together mitzvos]. The Maharal in Gevuros Hashem [chapter 50] explains that the anything could have been done to make a shinui. The additional reason of Tosfos [and of the Rambam] are coming to explain why specifically this was chosen as the shimui to be made.
In fact the Maharal in his haggada explains that in fact there is no shinui by dipping the karpas and eating at this point. Only once the children see the second dipping of the Maror will they question why there is an additional on this night.
The Rambam [Chametz U’Matzah 8:2] holds that everyone at the Seder must eat a kzayis of Karpas. However according to the other Rishonim not only do we not require a kzayis, in fact some hold [Shibolei Haleket] that only the one leading the Seder need eat Karpas, and not each participant, as this is sufficient to bring the children to ask.
There is a dispute among the Rishonim if leaning [heseiba] is required for the eating of Karpas [Shibolei Haleket / Avudraham]. Some have suggested that according to the Rambam that Karpas is a “mitvas achila” just as Matza and Maror, it would require heseiba as well. In fact the Brisker Rav who ate a kzayis in accordance with the opinion of the Rambam, in fact practiced heseiba while eating.
According to the Rambam we can understand why in the list of the order of the Seder, קדש ורחץ כרפס.., Karpas is mentioned, as this is also one of the mitzvos of the night, to eat a kzayis of Karpas. If this was just to make a shinui, it would not be mentioned in the order, just as the fact that we remove the table [or seder plate] and give sweets to the children is not mentioned.