The fifth chapter of Massekhet Eiruvin continues the discussion of eiruvei tehumim. The focus of this chapter is how we establish the boundaries of the city in order to measure the 2000 ama tehum that surrounds it.
The first Mishna asks Kaitzad Me’abberin et He-Arim – “How does one extend the boundaries of cities in order to ensure that all its protrusions are included within the borders of the city?” The Gemara explains that we draw straight lines running along the furthest-most dwelling-place on each side of the city, creating a rectangle around it. From here we will draw lines of 2000 amot from the city in each direction.
The interest of the Gemara focuses on the precise tradition of the language of the Mishna. Specifically, the Gemara tries to clarify whether the word me’abberin is written with the letter ayin or the letter alef.
The Gemara explains: The one who taught me’abberin with an alef explained the term in the sense of limb [ever] by limb. Determination of the city’s borders involves the addition of limbs to the core section of the city. And the one who taught me’abberin with an ayin explained the term in the sense of a pregnant woman [ubbera] whose belly protrudes. In similar fashion, all the city’s protrusions are incorporated in its Shabbat limit.
With an alef, the source of the word me’abberin would be ever – limb – like the limbs of a person that stretch beyond his body. According to the Aruk, we are similarly trying to add parts of the city that protrude beyond its center.
With an ayin the Me’iri explains that, as a pregnant woman who has in her womb a fetus that is an addition to her, we are similarly adding to the city beyond its established borders.
Establishing this tradition is so important to the Gemara, that Rabbi Yohanan is quoted as saying that he spent 18 days of growth studying with the great Rabbi Oshaya and he learned only one thing (or, perhaps, one thing in our Mishna) – that me’abberin was written with an alef.
The great Rabbi Oshaya is referred to in the Jerusalem Talmud as Rabbi Hoshaya Rabba, one of the most important sages of the period between the tannaim and amoraim. His major work was in the area of collecting the words of the tannaim in as faithful a fashion as possible, leading to the tradition that the only baraitot that could be relied upon were the ones that had been taught in the Bet Midrash of Rabbi Hoshaya and Rabbi Hiyya.
Rabbi Oshaya had many students, but the greatest of them was Rabbi Yohanan, who studied with him for many years. The comment in the Gemara that has Rabbi Yohanan studying with Rabbi Oshaya for 18 days must be referring to a very early stage in his career.