The opening section of Parashat Chukat discusses the basic laws of the para aduma, the red heifer which was burned to prepare ashes that were used for purification. Masekhet Para, the section of the Mishna which presents the detailed halakhot of the para aduma, begins with a debate among the Tanna’im regarding the minimum required age of the cow used as the para aduma. Rabbi Eliezer maintained that once a cow reaches its second year of life, it is considered a “para” – adult cow – and is no longer an “egla” (young calf). The majority view among the Tanna’im, however, maintained that the Biblical term “para” refers to a cow that is past its second year, and thus only at this point does a young cow become qualified to be used as a para aduma. As we would have expected, the Rambam follows the majority opinion, and rules that the para aduma must have completed two years of life (Hilkhot Para Aduma 1:1).
However, the Mishneh Le-melekh advances the theory that at least according to one view among the Rishonim, Rabbi Eliezer’s view is the accepted position. The basis for this theory is the second Mishna in Masekhet Para, which discusses the definition of the term “par” (“bull”) with respect to sacrifices. The Mishna cites the view of Rabbi Yossi that once a male bull has completed his first year, it is considered a “par” and thus qualifies for sacrifices that require a “par.” Then, the Mishna cites the majority view among the Tanna’im, but the precise text of the ruling is subject to some controversy. In many common editions, the majority view comments, “even in the third year” – indicating that they agree with Rabbi Yossi that a bull in its second year qualifies already as a “par.” According to this version of the text, the majority view simply clarifies that the bull can be older than one year old, and can even be already in its third year. If so, the Mishneh Le-melekh observes, then we must seemingly conclude that the majority view in this Mishna follows Rabbi Eliezer’s view in the previous Mishna, that a young cow becomes a “para” already after its first year. This might indicate, then, that whereas generally Halakha does not follow Rabbi Eliezer’s rulings in his disputes with the other Sages, in this instance, as evidenced by the second Mishna, Halakha indeed accepts his position, that a young cow qualifies as a para aduma already in its second year.
By contrast, the Rosh and the Vilna Gaon, in their respective commentaries to Masekhet Para, claim that the correct editions of the text omit the word “af” (“even”) from this Mishna. According to this version of the text, the majority view in the second Mishna is consistent with the majority view of the first Mishna, and maintains that a bull must complete two years of life before qualifying as a “par.” If we accept this text, then there is certainly no reason to believe that Halakha follows the minority opinion of Rabbi Eliezer.
Yet another possibility is to distinguish between cows and bulls, and this indeed is the view of the Rambam. In Hilkhot Para, as we have seen, the Rambam follows the majority view, that the para aduma must be in its third year of life. However, in Hilkhot Ma’aseh Ha-korbanot (1:14), he writes that a bull qualifies as a “par” with respect to sacrifices already in its second year. Following the first version of the text noted above, the Rambam maintained that a young bull becomes a “par” already after its first year, despite ruling that a female cow becomes a “para” only after its second year.