Both the groom and the bride need to acquiesce to the marriage. Daf TB Yevamot 113 compares and contrasts a minor girl and a deaf-mute when it comes to marriage. Since they are not legally competent to understand what is happening to them, the Torah doesn’t sanction their marriage because they can’t acquiesce. Life for a single woman was difficult. Without the protection of a husband and his family, she was easy prey to unscrupulous men or was without a means of support. For the protection of the minor girl and the female deaf-mute, the rabbis provided the necessary acquiescence so they could marry. Their marriage is on a rabbinic level and not a Torah level. Although both are married on a rabbinic level, daf TB Yevamot 113 list three major differences between a minor girl and a deaf-mute.

First of all, a minor girl may reject (me’oon) her husband, but a deaf-mute does not have the option of me’oon. “The Gemara asks: What is the difference between a minor girl, that she may perform refusal, i.e., she can retroactively nullify her marriage by means of a declaration of refusal of her husband, and a female deaf-mute, that she cannot perform refusal, as the Sages did not establish the option of refusal in her case? Since the marriage of a deaf-mute woman also applies by rabbinic law, why didn’t the Sages establish refusal in her case as well? The Gemara answers: The reason is that if so, i.e., had the Sages enacted refusal for a female deaf-mute, others would refrain from marrying her at all, as she can issue a declaration of refusal indefinitely, whereas in the case of a minor there is a time limit with regard to her option of a refusal.” (Sefaria.org translation)

Secondly, a minor girl married to a priest may eat teruma, but a deaf-mute may not. “What is the difference between a minor girl, that she may partake of teruma when she is married to a priest, and a deaf-mute woman, that she may not partake of teruma when she is married to a priest, despite the fact that both of their marriages apply by rabbinic law? As we learned in a mishna (Gittin 55b): Rabbi Yoḥanan ben Gudgada testified with regard to a female deaf-mute whose father married her off, that she can be divorced with a bill of divorce. And he testified with regard to a minor girl, daughter of a non-priest who was married to a priest, that she may partake of teruma, whereas a deaf-mute woman, it may be inferred, may not partake of teruma.

“Gemara answers: The reason that a deaf-mute woman may not partake of teruma, even if she is married to a halakhically competent priest, is due to a rabbinic decree lest a deaf-mute priest likewise feed teruma to his deaf-mute wife. The Gemara asks: And which prohibition would that violate? Let him feed her, as he is equivalent to a minor who eats meat from unslaughtered animals. This is referring to the halakha that there is no obligation to prevent minors from committing transgressions. Since a deaf-mute, who is not legally competent, has the status of a minor, the same reasoning should apply in this case. Consequently, the court should be under no obligation to prevent this deaf-mute woman from eating teruma unlawfully.

“Rather, it is a rabbinic decree lest a deaf-mute priest feed teruma to a halakhically competent wife. Since by Torah law her marriage to a deaf-mute man is not valid, she may not eat teruma. The Gemara asks: As well, in the case of a deaf-mute priest who wishes to feed a halakhically competent wife, let her partake of teruma that applies by rabbinic law. There are types of produce from which there is no obligation to separate teruma by Torah law, and one separates teruma from them due to rabbinic decree. Just as the marriage of this woman is by rabbinic law, she should be permitted to eat teruma that applies by rabbinic law. The Gemara answers: It is a rabbinic decree, as perhaps he will come to feed her teruma that applies by Torah law.” (Sefaria.org translation)

Last of all, a minor girl is entitled to a ketubah, the marriage contract which spells out the obligations of husband and wife to each other, while a deaf-mute is not entitled to a ketubah. Nevertheless, if the husband wishes to provide for one he may do so. “And what is the difference between a minor girl, that she has a marriage contract, and a deaf-mute woman, that she does not have a marriage contract? The Gemara answers: The reason is that if so, if the husband of a deaf-mute would be obligated to give her a marriage contract, men would refrain from marrying her at all.” (Sefaria.org translation)

There are two operating principles guiding the rabbis when making these distinctions. The first is the qualitative difference between a minor and a deaf-mute. The odds are in the minor’s favor that she will reach the age of majority and become legally competent. Especially before Helen Keller, the odds were against the deaf-mute’s ability to improve. She would remain legally incompetent all her life. Secondly, the rabbis wanted to encourage a sustainable marriage, by removing all the stumbling blocks that would discourage a man from marrying either a minor girl or deaf-mute.