Yevamot 58 - What does chuppah accomplish?
Normally, people get engaged and then marry under the chuppah. However, what happens when they do the chuppah without the prior engagement, and moreover, when they really should not get married, such as when a High Priest is marrying a widow. After this forbidden marriage she would lose the privileges of a Kohen's daughter (if she had them). Rav says: this chuppah is not legally significant, since there is a possibility that they will realize the wrongdoing and stop themselves. However, Shmuel says that the chuppah is too close to the transgression, and she lost the privileges already.
Rav Sheshet elucidated this disagreement from a seemingly unrelated ruling about a suspected wife. There, when she says "Amen, amen," this implies that not only she is saying the truth now, but she also never lied in other situations. But what other situation could the rule mean? After a few trials, we suggest that she was engaged, then hid with another man, then had a chuppah with the first one. But that is similar to our situation: he is forbidden to live with her until the situation is cleared, and they had a chuppah but did not live together. It could have been a brilliant resolution, but the Talmud asserts that the ruling itself is transmitted incorrectly, and cannot serve as any proof. The question remains unresolved.
Art: The Wedding Dress by George Goodwin Kilburne