Refer to 15:4:1:1*.

Sifra: To teach us that whatever is designated for Mishkav is subject to YTu'as Mishkav - to render Tamei Adam and Begadim, but, but not Adam. ¹

Sifra: To preclude a Ba'al Keri, an Even ha'Menuga'as, a Tamei Meis and a Meis from the Din of Mishkav and Moshav. ¹

Rashi and Targum Yonasan: To teach us that it the article is only subject to Tum'as Mishkav if it is designated exclusively for lying on or for sitting on, ¹ but not if one needs to ask the person who is lying or sitting on it to get up and allow the owner to use it for whatever it is designated for ('Amod ve'Na'aseh Melachteinu!')

Sifra: To preclude where the Zav sits or lies on a person - in which the person is not Metamei Adam and the clothes he is wearing.

Sifra: To teach us that Tum'as Mishkav u'Moshav applies even if the Zav lies on a chair or sits on a bed.

Sifra: It implies that the chair or the bed must be carrtying the majority of the Zav.

Rashbam: A Zav, a Zavah or a Nidah who is lying or sitting on a stone ¹ which is placed on top of a bed or sheet, which he is not touching (Even Mesamei), ² adopt Tum'as Mishkav or Tum'as Moshav, to be Metamei a person and Keilim.

Sifra: To include in the Din of Mishkav and Moshav, someone who lies on a seat or who sits on a bed, and someone who stands hangs or leans on on anything that is made to bear one's weight.

Moshav Zekenim (in Pasuk 33, citing the Rambam): It is through sitting, lying, hanging, leaning or being carried on it.