Shabbat 43 - Corpse in the sun
If one has an oil lamp that is leaking oil, he nevertheless may not put a plate next to the lamp, in order to collect the dripping oil. Why not? - The oil in the lamp is designated to be burned on Shabbat, and it is not designated for consumption. Therefore, the oil is considered "not prepared for use," or "muktzeh", and muktzeh objects cannot be handled or used on Shabbat. When one puts a plate to collect the oil, he effectively "cements" the plate to the floor: since the plate with the muktzeh oil may be not carried any longer, it is as if glued to the floor, and he has thus performed the prohibited labor of building on Shabbat.
Another possible explanation is that he would be moving a non-muktzeh object (plate) for the sake of a muktzeh object (oil), and that too would be prohibited. However, that question, can one move a non-muktzeh object for the sake of a muktzeh object, is itself a subject of disagreement. Let's look at a couple examples.
One may want to put a basket under a hen, so that its egg would not fall and break on Shabbat. That, however, is prohibited, just as putting a plate under dripping oil. However, one can put an overturned basket to cover the egg, even though this is using a permitted object for the sake of forbidden. Can we thus use permitted objects for the sake of muktzeh? - No, this is a special dispensation, to prevent a commonly occurring loss.
If a dead body is lying in the sun on Shabbat, two people can come and sit by its sides. When it gets hot for them, they bring mats and sit on them. This establishes that they care for the themselves, not for the dead. Then, if it is still hot, they can bring a tent and place it over themselves (and the dead). Then they can leave, and the dead is protected. Are we using a permitted object for the sake a muktzeh (corpse)? - No, they use it for themselves. Then do we see that moving a permitted object for the sake of a muktzeh is NOT allowed? - Really, it is, but the procedure with the corpse also became law.
Art: Baldassare De Caro - A Cockerel And Chickens In A Shed With An Earthenware Bowl And Baskets With Eggs