(a) Mordechai, that is an excellent question. In fact, the Ran (Shabbos 128b, 51b in the pages of the Rif, cited by the Tosfos Yom Tov on the Mishnah in the 23rd Perek) brings that very proof to show that it is prohibited to move even part of an object that is Muktzah, just as you wrote.

However, the Ran points out that this seems to contradict the teaching of the Gemara in Shabbos 128b. We find there that it is permitted to drive an animal back into its pen using the tactic of Medadim, which means grasping it by its neck or wings or flanks and shoving it in the proper direction. Why should this be permitted? One is moving the limbs of an animal! The Ran answers that Chazal only permitted Medadim when the animal needs it urgently, because of Tza'ar Ba'alei Chayim. This seems to support your view and oppose the view of Rav Gustman zt'l.

(b) But I would like to point out that none of the Poskim who cite this Halachah pose any restrictions to Medadim (see Rosh, Rambam Hilchos Shabbos 25:26) - which implies that they did not accept the argument of the Ran. They apparently permitted Medadim under all circumstances, because one is not moving the entire object of Muktzah, just a part of it. This, then, is the view of Rav Gustman zt'l.

The Shevisas ha'Shabbos (Kotzer #37) brings further support for this view from a Tosefta (Shabbos 17), cited by the Shulchan Aruch (OC 302:11), which allows using the tail of a horse to wipe one's self (see Bi'ur Halachah there, who has great difficulty with this Halachah). He also points out that it is permitted to milk a cow on Shabbos (Ran, beginning of Beitzah) even though the cow itself is Muktzah. (To justify the opinion of the Ran, the Shevisas ha'Shabbos suggests that the Ran may permit moving part of an object that is Muktzah in these cases since it is being moved for the benefit of something that is not Muktzah, and not for the benefit of the object of Muktzah itself - as we find with regard to Tiltul Min ha'Tzad.)

(c) How, though, would the other Rishonim, who permit moving part of an animal that is Muktzah, answer the question of the Ran from the Mishnah which prohibits moving even a single limb of a dead person (Shabbos 151a)?

It would seem logical to differentiate between a live being and a dead object. A limb of a live being is indeed only "part" of a Muktzah object, since it cannot be detached from the rest of the living being (such as an animal or growing plant) without changing it inherently into a different type of object (i.e. removing the life from it). However, one side of a broken tire is no different from the other side. If the tire is Muktzah it will be prohibited to lift even part of it, since that part can be removed and looked at as an object unto itself, ignoring the rest of the tire. The same applies to moving a limb from a corpse. (Upon searching, I found that Harav Yosef Ben Arza, from our Kollel, presented a similar logic in his Yosef Da'as for Shabbos 128b.)

It may also be permitted to move the door of a house, even though the house is not a "live" being, since it too is separate and apart from the rest of the house: The rest of the house cannot be moved (because it is attached to the ground), only the door can be moved. Thus, the door is inherently different from the rest of the house and thus by moving it one is moving only part of an object that is Muktzah. (Teshuvos Beis Yehudah #11 - Rav Yehudah Ayash - uses such a logic to permit moving any object that is Mechubar l'Karka - as is implied by the Chidushei ha'Ran in Shabbos 82a regarding wiping one's self with plants.)

Best wishes,

Mordecai Kornfeld

Kollel Iyun Hadaf