יז אימר דאמרינן אתי עשה ודחי לא תעשה לא תעשה גרידא לא תעשה שיש בו כרת מי דחי ותו לא תעשה גרידא מנלן דדחי
17 so that their rivals also<span class="x" onmousemove="('comment',' If they and their rivals were married to a stranger. ');"><sup>26</sup></span> are forbidden,<span class="x" onmousemove="('comment',' To marry the man whom the forbidden relatives themselves are not allowed to marry. ');"><sup>27</sup></span> hence it must be stated:<span class="x" onmousemove="('comment',' Lit., 'say'. ');"><sup>28</sup></span> As a wife's sister is singled out in that she is a forbidden relative, <i>kareth</i> is incurred for presumptuous intercourse with her and a sin-offering for unwitting intercourse, she may be married to the other brothers, but is forbidden to the levir, and her rival is forbidden, so also in the case of any woman who is a forbidden relative, for presumptuous intercourse with whom is incurred the penalty of <i>kareth</i> and for unwitting intercourse a sin-offering, who may marry one of the other brothers, but is forbidden to the levir, her rival also is forbidden; excluded, however, are the six more rigidly forbidden relatives. Since they may not be married to the other brothers, their rivals are permitted; for [the law of] 'rival'<span class="x" onmousemove="('comment',' I.e., the rival's exemption from the levirate marriage and halizah. ');"><sup>29</sup></span> is applicable only [to widows] of a brother.<span class="x" onmousemove="('comment',' Where one of the widows is a forbidden relative of one of the surviving brothers and no forbidden relative of the deceased. As the relative is forbidden to marry the brother, her rival also is forbidden to him as 'his brother's wife'. Where the relative, however, is married to a stranger, her rival is permitted to those to whom the relative herself is forbidden. ');"><sup>30</sup></span> Thus we have deduced the prohibition. Whence, however, is the penalty inferred? — Scripture said, For whosoever shall do any of these abominations etc. [shall be cut off from among their people.]<span class="x" onmousemove="('comment',' Lev. XVIII, 29. ');"><sup>31</sup></span> The reason,<span class="x" onmousemove="('comment',' Why a wife's sister is forbidden the levirate marriage. ');"><sup>32</sup></span> then, is because the All Merciful has written, ''aleha',<span class="x" onmousemove="('comment',' V. the texts from Lev. and Deut. and the analogy supra. ');"><sup>33</sup></span> otherwise it would have been said that levirate marriage may be contracted with the wife's sister; what is the reason? Is it because we assume that a positive precept,<span class="x" onmousemove="('comment',' The commandment of the levirate marriage. ');"><sup>34</sup></span> supersedes a negative precept?<span class="x" onmousemove="('comment',' The prohibition to marry one's wife's sister. ');"><sup>35</sup></span> Surely, it is possible that<span class="x" onmousemove="('comment',' Lit., 'say'. ');"><sup>36</sup></span> the rule that a positive precept supersedes a negative precept applies only where the latter is a mere prohibition; does it, however, supersede a prohibition involving the penalty of <i>kareth</i>?<span class="x" onmousemove="('comment',' The prohibition to marry one's wife's sister. ');"><sup>35</sup></span> Furthermore, whence is it derived that it may supersede even a mere prohibition?