Yevamot 30 - What does the intent to marry accomplish?
We saw that the Sages instituted "an intent to marry" in the case of yibum, which looks like regular engagement . Note, however, that the couple is already married in some sense: the mitzvah of yibum is accomplished by an intercourse, and strictly speaking no other formalities are required. Therefore, what does the declaration of this intent accomplish, an engagement or a complete marriage?
That was the question posed by Rabbah. Abaye asked - for what practical purpose are we asking? If it is for a Kohen to allow him to bury her if she dies - the answer is clear: even for a real engaged bride a Kohen is not allowed to go to the cemetery, and certainly not for one with whom there is only an intent to marry. And if the question is, do we need a chuppah marriage ceremony, then the answer is clear also: he could do a yibum even against her will, so now that he made a declaration, does it make it any worse? Of course he does not need a chuppah!
However, Rabbah answered that this is not so simple. Before the declaration he indeed had the right to do yibum. But now that he made it, maybe he lost this right, got the right of a mere engagement instead and does need a chuppah.
The question remains without a conclusive proof, and besides it concerns only the opinion of Beit Shammai, while the practical law always accords with the opposing opinion of Beit Hillel.
Art: The Bride by Edward Alfred Angelo Goodall