When someone mistakenly makes a concession in a business deal – a situation that the Gemara calls mehila be-ta’ut (mistaken forgiveness) – must he abide by his word or can he claim that he is not responsible for something that he agreed to by mistake? The Gemara (on daf 66b) discusses Rav Nahman’s position on this question, based on his ruling that someone who sells his date crop before the fruits have developed can back out of the sale, since ein adam makneh davar she-lo ba la-olam – a person cannot sell something that does not yet exist. Nevertheless, Rav Nahman agrees that if the purchaser takes the fruit we do not force him to return them, since the owner agreed to the sale, albeit mistakenly.
On our daf, Rava tells that when he was studying with Rav Nahman, he wanted to challenge this ruling based on the law of ona’a (exploitation), but Rav Nahman realized what he was about to ask and said “but ailonit disproves your point.” The Gemara explains that Rava wanted to argue that even if a person agreed to pay an unreasonable price for something (the case of ona’a), Jewish law does not allow him to make that mistake, and the sale is recalled. In response, Rav Nahman referred to a case of ailonit – a woman who never matures physically, and whose marriage is consequently annulled – whose erstwhile husband retains some of the agreed upon financial benefits of their marriage.
From the detailed discussions in the Gemara – mainly in Massekhet Yevamot – it appears that an ailonit suffers from a genetic defect that does not allow her to have children. This is a different categorization than an akara – a barren woman – whose physical and sexual development is ordinarily normal, but cannot have children because of some other deficiency or impediment. From those descriptions it appears that an ailonit can be recognized by certain unique physical traits, including a lack of secondary sex characteristics like pubic hairs. Furthermore, it appears from the Gemara that there are different types of ailonit, ranging from women who have an overabundance of male hormones to those who suffer from Turner syndrome, where only one X chromosome is present and fully functioning. Approximately 98% of all fetuses with Turner syndrome spontaneously abort; the incidence of Turner syndrome in live female births is believed to be about 1 in 2500.