SEIF 7 (CONTINUED)
BOSIS NOT ON THE MAIN PART OF UTENSIL
If Muktza was placed on a secondary part of a utensil, but there was nothing on it's main part, the Trumas Hadeshen says that it's not Bosis and you may move the utensil. He brings a proof from the Gemara Shabbos 44b. If someone puts money on a wheel that is removed from the wagon, the wheel becomes Bosis to it. Tosfos explains that if the wheel would be attached to the wagon, the money on top of it would not make it Bosis. Therefore we see, if it's not on the main part of the utensil, it's not Bosis. So if a pocket is sewed onto clothes, Muktza in the pockets do not render the clothes Bosis.
The Rama says, therefore, if one forgot Muktza in his pockets, you may move the clothes. The Magen Avraham asks, that by forgetting, even if the Muktza is on the main part of the utensil it doesn't become Bosis? You cannot answer that in the case that it's not on the main part you're allowed to move it without shaking off the Muktza first, since the Rambam says, in our case, you need to shake it off. Also, we see that Tosfos learns that our case refers to leaving the money on purpose, and not like the Rama says, that he forgot it there.
(But Rav Akiva Eiger brings a proof from Tosfos and the Rashba that they hold if you forgot it on the wheel, you don't need to shake it off. Since they ask: Why didn't the Gemara say the case is where you forgot it on it and when it's attached you don't need to even shake it off before you move it? The Rashba answers that the implications are that you may move it only when it's attached in all cases, even if you only moving it because you need it's place (where if you forgot it there, you wouldn't need to shake it off, since you wouldn't be able to facilitate that place while the Muktza is lying there.) But if they would hold like the Rambam, there would be no question to begin with.)
So the Magen Avraham answers, the Rama is only saying that the case is if you forgot to take the Muktza out of your pocket, since L'Chatchila you shouldn't leave it there on Shabbos, lest you'll wear it and forget to shake it out before you leave your house and end up carrying it. The Shaar Hatzion doesn't understand where is the Magen Avraham Mekor to make such a Gezeira. Therefore he opts to say that the explanation of the Rama is that he holds like Tosfos (that Rav Akiva Eiger brought) that you don't even need to shake it off if you forgot it there.