1) APPRAISING UNPLANTABLE PARTS OF A FIELD
QUESTION: The Gemara quotes the Mishnah in Erchin (25a) which teaches that if a field contains pits deeper than ten Tefachim, or rocks higher than ten Tefachim, those areas are not calculated together with the field in accordance with the prescribed formula of "Zera Chomer Se'orim." (The Torah teaches (Vayikra 27:16) that one who consecrates his field (when the laws of Yovel are in force) may redeem his field by paying an amount calculated according to the formula of fifty silver Shekalim for every Chomer of barley seed that can be planted there.) The Gemara asks that although the value of the pits and rocks are not calculated with the field, they should become Hekdesh in their own right. Mar Ukva bar Chama answers that the Mishnah in Erchin refers to a pit filled with water which is completely unfit for planting. The Gemara asks that if the pit is filled with water, it should not be included as part of the field even if it is less than ten Tefachim deep. The Gemara answers that pits less than ten Tefachim deep are considered "basins" of the field and thus remain part of the field.
The Gemara concludes that the formula of "Zera Chomer Se'orim" is used for appraising the value of a field only when the field is arable. When it is not fit to be sowed, the field is evaluated according to its market value. According to the Gemara's conclusion, why is a pit less than ten Tefachim appraised together with the field? Even though it is less than ten Tefachim deep, since the pit is filled with water it is not fit for sowing, and it should not be evaluated in the manner of a plantable field.
ANSWER: Ten Tefachim is the minimum height which an area needs in order to have the status of an independent domain. For example, the laws of Shabbos state that an area is considered an independent Reshus ha'Yachid only when it has a height (or depth) of ten Tefachim. One who carries from a private domain which lacks that height into Reshus ha'Rabim does not transgress the Isur d'Oraisa of Hotza'ah on Shabbos. In the case of the Gemara here, a pit which is ten Tefachim deep is an independent domain. Accordingly, if an area must be fit for sowing in order to be redeemed according to the Torah's prescribed formula, the pit must be judged independently (since it is an independent domain from the field). When the pit is full of water it is not considered fit for sowing.
In contrast, when the pit is less than ten Tefachim, it does not have the status of an independent domain and is still considered part of the field. Since the rest of the field is fit for sowing, the pit is evaluated according to the way the entire field is evaluated. (See RASHBA.)

61b----------------------------------------61b

2) THE POSITIVE AND NEGATIVE ELEMENTS OF A "TENAI"
QUESTION: The Mishnah (61a) quotes Rebbi Meir who maintains that every statement of Tenai (condition) must be "like the Tenai of Bnei Gad and Bnei Reuven." The Gemara cites proof for Rebbi Meir's opinion from the verses which discuss the Tenai that Avraham Avinu stated when he made Eliezer swear that he would travel to Avraham's family to seek a wife for Yitzchak.
RASHI (DH bi'Shlama) explains the Gemara's proof. Rebbi Meir maintains that a statement of Tenai must include explicit mention of both the positive and negative elements; mention of one does not imply the other. Avraham Avinu said that Eliezer would be subject to the oath (or "curse") "if you do not go to my father's house and to my family and take a wife for my son" (Bereishis 24:38). Although this statement implies that if Eliezer does go, he will not be subject to the oath, nevertheless Avraham Avinu explicitly added that "you will take a wife for my son from my family and from my father's house, and you will be absolved from my oath" (24:40-41). Avraham Avinu's explicit mention of both the positive and negative elements of the oath teaches that every Tenai must express both the positive and negative elements and one cannot be inferred from the other.
In his comments on the Mishnah, RASHI (61a, DH k'Tenai) lists three requirements of a verbally-stated condition (according to Rebbi Meir): The condition must be doubled ("Tenai Kaful") and express both the positive and negative elements of the Tenai, the positive element must precede the negative element ("Hen Kodem l'Lav"), and mention of the actual condition must be made before mention of the act that will take effect ("Tenai Kodem l'Ma'aseh").
However, in the case of Avraham Avinu and Eliezer, the "Lav" was stated before the "Hen." The negative ("if you do not go," Bereishis 24:38) preceded the positive ("you will take a wife for my son from my family and from my father's house, and you will be absolved from my oath," 24:40-41)! Why does the Gemara cite these verses as proof for Rebbi Meir's opinion?
ANSWER: The elements of "Hen" and "Lav" are not judged according to the positive and negative expressions of "yes" and "no" or "do this" and "do not do this." Rather, the elements of "Hen" and "Lav" are judged according to the act being done. "Hen" represents that which will make the act take effect. "Lav" represents that which will make the act not take effect. The "positive" and "negative" elements of a condition refer to whether those elements establish the act ("Hen") or nullify it ("Lav").
In the case of Avraham Avinu and Eliezer, the act which was contingent on the Tenai was the oath (including the severity and awe which would accompany it were it to take effect). Avraham Avinu deemed it necessary to administer an oath because of his concern that Eliezer would not seek a wife for Yitzchak from Avraham Avinu's family. The establishment of the oath depended on Eliezer's not going. Accordingly, his not going was considered the "Hen" (since, by not going, the oath would take effect). If, on the other hand, Eliezer would go but would be unsuccessful in finding a wife for Yitzchak, the oath would not take effect. Hence, Eliezer's going was considered the "Lav."
A similar explanation is suggested by the RASHASH to answer the question of TOSFOS (62a, DH bi'Shlama). In the case which Tosfos cites, the Kohen states that if the Sotah did not commit adultery, she will be exonerated by the drinking of the Mei Sotah, but if she did commit adultery, she will be punished. Tosfos asks that this condition seems to place the "Lav" before the "Hen."
The Rashash answers that the act achieved through the drinking of the Mei Sotah is the woman's vindication. Her vindication is achieved only if she did not sin. Although this contingency (if she did not sin) is phrased in the negative sense, it is considered the positive element of the condition since it accomplishes the woman's exoneration (which is certainly positive). Any contingency which causes the act to take effect -- whether through positive or negative action -- is considered the "Hen" element of the condition. (A. Kronengold)
3) INFERRING A CURSE FROM A BLESSING
QUESTION: The Mishnah (61a) quotes Rebbi Meir who maintains that every statement of Tenai (condition) must be "like the Tenai of Bnei Gad and Bnei Reuven." The Gemara cites proof for Rebbi Meir's opinion from the verses which discuss the blessings promised to the Jewish people if they follow Hash-m's will (Vayikra 26:3-13) and the verses which discuss the curses if they do not follow His will (Vayikra 26:15-43). The fact that the Torah explicitly states the curses, which are the converse of the blessings, and does not infer them is proof for Rebbi Meir's opinion.
What is the Gemara's proof for Rebbi Meir's opinion from these verses? Since the curses far outnumber the blessings, it is impossible to infer all of the curses from the list of blessings.
ANSWER: The PNEI YEHOSHUA answers that the Gemara's proof indeed is only from the curses which are the exact converse of the blessings stated and thus could have been derived through inference. The other curses, which have no parallel in the list of blessings, certainly must be stated explicitly.