Shabbat 93 - Giant loaf of bread

If one takes a loaf of bread and carries it from his home to the street, then, of course, he is liable for violating Shabbat. We learned it throughout this chapter. 

If, however, two people carry the loaf together, neither of them is liable. Why is that? To be liable, one has to complete the action of a Shabat violation by "committing it that may not be done." The grammar points to him committing the act entirely without any help.

What if the loaf was so big that neither one nor the other could carry it alone, and they had to carry it together? They are again liable. Here, however, Rabbi Shimon considers them both exempt. Both Rabbi Shimon and his opponents are based on the same phrase. However, they disagree on what exactly the other phrases exclude from liability.

Art: Still life with stoneware jug, wine glass, herring, and bread by Pieter Claesz