The second Mishna in the perek discusses a case of someone who built his sukka by resting it on the legs of a bed – al karei ha-mitah. The Tanna Kamma rules that the sukka is fit for use; Rabbi Yehuda rules that if the sukka cannot stand on its own it is disqualified.
Several explanations are given that attempt to clarify the case of building a sukka al karei ha-mitah. Most commentaries appear to accept the definition offered by the Talmud Yerushalmi that the bed is part of the sukka – in effect, the floor of the sukka. According to the Tosafot Ri”d, we are talking about a case where the bed is so large that it is the size of a kosher sukka, and the s’khakh is being placed on the four poles that extend up from the head and foot of the bed. A similar explanation has the bed acting as support for the sukka on one side.
The Ra’avad disagrees, and offers an alternative understanding of the case in the Mishna. He argues that the bed is not part of the structure of the sukka at all; the supports for the roofing are merely resting on the bed. The concern is that if the bed falls down or is removed, without the support offered by the bed the entire sukka may collapse. The Ramban offers another approach, suggesting that we are talking about a case where the legs of the bed are ten tefahim high (i.e. the minimum height of a kosher sukka), and that the bed is turned over so that its legs are used to hold the s’khakh. The concern in this case is that the bed might be removed by someone who wants to use it for its actual purpose.
As far as Rabbi Yehuda’s position is concerned – that if the sukka cannot stand on its own it is disqualified – the Rosh sees this comment as a clarification, rather than a disagreement with the position of the Tanna Kamma. Other commentaries disagree, and according to them it is not clear whether halakha follows the opinion of the Tanna Kamma or that of Rabbi Yehuda.