The mishna and the braita have different versions of Rabbi Yehuda's opinion regarding Rabban Gamliel's approach to Sadducees and eruvin. One implies the law regarding Jews is true for them that they can relinquish their rights and the other seems to hold that they are treated as gentiles. How is this contradiction reconciled? What makes someone considered a mumar, an apostate for all laws of the Torah? Is there a different definition for eruv than for other areas of law? If there is a courtyard in which one or more members did not join the eruv, how can one relinquish their rights and what then is permitted in the courtyard? The mishna brings a number of different scenarios and the gemara begins to analyze the different cases.