Rava raises an apparent oddity in a situation of marriage. According to Rava, if a man says to a woman “you are betrothed to half of me” the marriage takes effect; if he says to her, however, “half of you is betrothed to me” the marriage does not work. In response to Abaye’s objection that the Torah describes marriage in the words, “Ki yikah ish ishah – when a man takes a woman as his wife” – indicating that both husband and wife are full and complete, Rava explains that since according to the letter of the law a man can marry more than one woman, therefore the statement “you are betrothed to half of me” has meaning. A woman can be married to one man only, so saying “half of you is betrothed to me” has no meaning whatsoever.
One question raised by the commentaries is why the man would need to make a statement that he retains the right to marry an additional woman (the interpretation given by Rava to his statement that only half of him will be married to her). Biblical law allows him to marry a second wife, so there should be no reason to include such a statement as a condition of the marriage!
Tosafot R”i haZaken points out that ordinarily a person can only take a second wife if he has the means to support both. Making such a condition allows him to marry a second wife under all situations. The Ritva essentially agrees with this approach, adding that stating the condition will at least protect the husband from his first wife’s objections to a second marriage, or it might allow him to marry a second time even in communities where such a practice was not accepted.
A student of the Rashba argues that this statement is not necessary; the point of the Gemara is to teach us that even a lashon geru’ah – a weak expression of marriage – will, nevertheless create a full marital relationship as long as the statement does not detract from the marriage itself.