Why does Naomi talk in masculine form to her daughters-in-law?

Question

In Rus 1:8, Naomi is telling her two daughters-in-law that they should return to their homes.

וַתֹּ֤אמֶר נָעֳמִי֙ לִשְׁתֵּ֣י כַלֹּתֶ֔יהָ לֵ֣כְנָה שֹּׁ֔בְנָה אִשָּׁ֖ה לְבֵ֣ית אִמָּ֑הּ יעשה [יַ֣עַשׂ] יְהוָ֤ה עִמָּכֶם֙ חֶ֔סֶד כַּאֲשֶׁ֧ר עֲשִׂיתֶ֛ם עִם־הַמֵּתִ֖ים וְעִמָּדִֽי׃

But Naomi said to her two daughters-in-law, “Turn back, each of you to her mother’s house. May the LORD deal kindly with you, as you have dealt with the dead and with me!

How come she uses the masculine form of the bolded words instead of the feminine form (עִמָּכֶן and עֲשִׂיתֶ֛ן) when she is speaking to females?

Answer 1

According to the commentary of the medieval rabbinic grammarian, R. Yosef Caspi, in biblical Hebrew, women are occasionally addressed in either masculine or feminine verb endings:

ואין קושייא מאמרו אלו הכנויים לאלו הנשים פעם בדרך לשון זכר , כמו "עמכם" , "עשיתם" (לעיל , ח) , "והֵמה" (להלן , כב); ופעם לשון נקבה , כמו "לכנה" , "שובנה" (לעיל , ח) , ומצאן , ורבים זולת זה - כי כבר הודעתיך יסוד זה (מ"כ ח"ב ע' 20 - 21 ).

There is no difficulty in that sometimes women are referred to these in the masculine form...and sometimes in the feminine form.

Alternatively, R. Shlomo Alkabetz (author of "Lecha Dodi"), in his commentary to Ruth (Shoresh Yishai), reads the the masculine form midrashically -- that the words with a final mem instead of a final feminine nun hints that Hashem would reward them for the forty steps the women took in accompanying Naomi thus far toward her journey back (the letter mem has the numerical value of the number forty):

אולם אומרו עמכם במ"ם וכן כאשר עשיתם במ"ם ואם הוא סימן זכרות לא נקבות אפשר שכיונה כי עד העת ההיא הלכו עמה מ' פסיעות כדאמרינן במדרש רות רבה ב כ ר' ברכיה בשם ר' יצחק ארבעים פסיעות הלכה ערפה עם חמותה ונתלה לבנה ארבעים יום שנאמר שמואל א' יז טז רגש הפלשתי השכם והערב ויתיצב ארבעים יום ע"כ ובהיותה כעת בדלי דלות ולא מצאה ידה די השב להן גמולן אמרה כי בעל הגמול יגמול להן שכר הפסיעות ההנה כי ארבעים ישי הנה ולכן אמר יעש ה' עמכם וכאשר עשיתם כי בפירוש אמרה על התכריכין ועל ויתור הכתובות כמדובר ובסתום הודיעה שאפילו שכר פסיעות תטולנה וכי הנן ספורות והן ארבעים

It says "with you" and "as you have dealt" with a mem. If this is a masculine, and not feminine form, it can be explained that they walked with her forty steps as it is says in the Midrash Rabba of Ruth in the name of R. Yitzhak: Orpah walked forty steps with her mother-in-law...therefore, Hashem will reward you...even these steps taken which amounted to forty.

Lastly, R. Shmuel Yerushami, who is the author of the modern Me'am Lo'ez commentary to Rut, suggests that it's masculine because the women had strong characters, which the Yerushalmi considers "manly". I'm not joking:

שנכתב בלשון זכר, לרמוז שהיו נשים גברתניות, היינו בעלות רצון חזק. ועוד שהיא שיבחה את מדותיהן, שזה שנתקרבו לחסות תחת כנפי השכינה לא היה מתוך פניה כל שהיא, אלא היו בעלות מדות טובות גם קודם לכן, והראיה שעשו חסד עם החיים ועם התמים, וזה מעיד על בור לבבם עם ה׳ ואנשים

It's written in the masculine form to hint at the women's manliness, as they had a strong will. Ruth was thus praising their virtues...that they had good virtues even beforehand, and the evidence that they did acts of loving-kindness with both the living and the dead, testified to the purity of their heart for Hashem and man.

Answer 2

Holmstedt's grammatical description of Ruth (Ruth: A Handbook on the Hebrew Text) states for 1:8:

The use of morphologically masculine affixes when the referents are clearly feminine, Ruth and Orpah, is not typical although it is attested elsewhere (see GKC §135o; JM §149–50). In Ruth this happens mostly in the mouth of No‘omi (see also 1:9, 11, 13), although the narrator and the “people of Bethlehem” both use the masculine-for-feminine, twice for the narrator (שתיהם 1.19 and המה 1:22) and once for the Bethlehemites (4:11 שתיהם) in each case the forms refer to two women. Neither Ruth nor Boaz utter the gender switch and even the narrator’s one switch in 1:19 is followed by multiple cases of 3fpl affixes. Moreover, while No‘omi uses a 2mpl qatal verb here in v. 8, she uses 2fpl yiqtol and imperative verbs throughout her speech in this section. It is thus difficult to discern either a grammatical or stylistic reason for the variation. Arguments that the forms reflect dialectal variation or a vestigal feminine dual (Campbell 1975:65) do not explain why the expected -ן suffixes for two females are used elsewhere (1:9, 19 [3x]). It is possible that the narrator uses marginal language to give the book a foreign or perhaps archaic coloring. The number of cases could not have been too many, though, or the language would have interfered with the narrative rather than contributing to it; this might explain the handful of cases.

It may also be an example of gender neutralization, wherein the less frequent feminine forms are replaced colloquially with the masculine forms.