מתני׳ הכל שוחטין ושחיטתן כשרה חוץ מחרש שוטה וקטן שמא יקלקלו את שחיטתן וכולן ששחטו ואחרים רואין אותן שחיטתן כשרה:
MISHNA: Everyone slaughters an animal, i.e., can perform halakhically valid slaughter, and their slaughter is valid, except for a deaf-mute, an imbecile, and a minor, lest they ruin their slaughter because they lack competence. And for all of them, when they slaughtered an animal and others see and supervise them, their slaughter is valid.
גמ׳ הכל שוחטין לכתחלה ושחיטתן כשרה דיעבד
GEMARA: There is an apparent contradiction between the first two phrases of the mishna. The tanna begins: Everyone slaughters an animal, indicating that their performing slaughter is permitted ab initio, and then teaches: And their slaughter is valid, indicating that their slaughter is valid only after the fact.
אמר ליה רב אחא בריה דרבא לרב אשי וכל הכל לכתחלה הוא אלא מעתה הכל ממירין אחד האנשים ואחד הנשים ה"נ דלכתחלה הוא והא כתיב (ויקרא כז, י) לא יחליפנו ולא ימיר אותו טוב ברע או רע בטוב
Rav Aḥa, son of Rava, said to Rav Ashi: And does every use of the term: Everyone, indicate that the action in question is permitted ab initio? If that is so, in the mishna (Temura 2a), where it says: Everyone substitutes a non-sacred animal for a sacrificial animal, both men and women, is that also an expression indicating that it is permitted ab initio? But isn’t it written: “He shall neither exchange it, nor substitute it, good for bad, or bad for good” (Leviticus 27:10)?
התם כדקתני טעמא לא שהאדם רשאי להמיר אלא שאם המיר מומר וסופג את הארבעים
Rav Ashi answers: There, the reason the mishna uses the word everyone is that it immediately teaches: That is not to say that it is permitted for a person to substitute; rather, it means that if one did substitute a non-sacred animal for a sacrificial animal, substitution takes effect, and the one who substituted the non-sacred animal incurs [vesofeg] the forty lashes that are the punishment for violating the prohibition “Nor substitute it.” But here, since the mishna does not similarly qualify its statement, it indicates that everyone may perform the slaughter ab initio.
אלא הכל מעריכין ונערכין נודרין ונידרין הכי נמי דלכתחלה והא כתיב (דברים כג, כג) וכי תחדל לנדור לא יהיה בך חטא
Rav Aḥa challenges: But a mishna teaches (Arakhin 2a): Everyone takes vows of valuation and is thereby obligated to donate to the Temple treasury the value fixed by the Torah based on the age and gender of the person valuated; and everyone is valuated, and therefore one who vowed to donate his fixed value is obligated to pay; everyone vows to donate the market value of a person as a slave to the Temple treasury and is thereby obligated to pay; and everyone is the object of a vow if others vowed to donate his market value. Is that also an expression indicating that it is permitted ab initio? But it is written: “And if you shall cease to vow, there shall be no sin in you” (Deuteronomy 23:23), indicating that it is preferable not to vow.
וכתיב (קהלת ה, ד) טוב אשר לא תדור משתדור ולא תשלם ותניא טוב מזה ומזה שאינו נודר כל עיקר דברי רבי מאיר ר' יהודה אומר טוב מזה ומזה נודר ומשלם ואפי' רבי יהודה לא קאמר אלא באומר הרי זו אבל
And it is written: “It is better that you should not vow, than that you should vow and not pay” (Ecclesiastes 5:4); and it is taught in a baraita with regard to that verse: Better than both this one, who vows and does not pay, and that one, who vows and pays, is one who does not take a vow at all; this is the statement of Rabbi Meir. Rabbi Yehuda says: Better than both this one, who vows and does not pay, and that one, who does not vow at all, is one who vows and pays in fulfillment of that vow. Rav Aḥa comments: And even Rabbi Yehuda states his opinion only in a case where one vows and says: This animal is designated for sacrifice, as in that case there is no concern that he will fail to fulfill his commitment, since even if the animal is stolen or lost, he is not required to bring another in its place.