If grain or vegetables are planted in a vineyard, then the many of the vines become forbidden from gaining any benefit and must be burnt (see 5:5). Furthermore, even if a product that is kilayim grew on its own, if the owner is aware of its presence and leaves it there, the vines will also become prohibited. The Mishnah (5:6) taught that in such a case, if the owner has not yet reached the kilayim as he works in the field and declares that he will remove it when he reaches that point, then the vineyard remains unaffected. If however the owner states that he will deal with it at a later time, then if the product grows one two-hundredth1 of its size, then the vines are assur. This is because he has demonstrated that, at least momentarily, he is happy for the kilayim to remain. We shall analyse this measure of a two-hundredth.
Rashi (Pesachim 25a) explains that if produce that became forbidden due to kilayim is mixed with other produce, it is only batel (annulled) in the mixture when there is a ratio of two-hundred parts to one. Consequently, in our case until it has grown enough such that the ratio is reduced, the kilayim growth is batel in the permitted parts. This is because only that which grows after the owner’s knowledge is prohibited.
Another case is mentioned that has a similar law (Bava Batra 2a). If a fence that divides a field and a vineyard falls, the owner of the vineyard is instructed to fix the fence. If he does not, then if the produce grows one two-hundredth, the produce is assur. Rabbeinu Tam adds that if the fence fell twice, and each time the produce grew less than one two-hundredth before the fence was fixed, even though the total growth is greater than the limit, the produce is mutar. The reason is that after the first instance, the growth was already considered batel before the fence fell a second time.
The position of the Rabbeinu Tam raises an interesting question. The Gemara (Avoda Zara 73a) teaches that if a small amount of yayin nesech (wine used for idol worship) continually drips into a barrel of permitted wine, the mixture is permitted. The reason is that each drop is batel in the barrel prior to the next one.2 Now recall that Rashi explained that in our case the measure of one two-hundredth is because of the laws of bitul.If in the case of yayin nesech,*each drop could be considered batel prior to the one that followed, then in our case as well, each microscopic growth of issur kilayim should be considered batel*!
The Tosfot (Bava Kama 100b) cites Rabbein Tam’s answer that in the case of yayin nesech there is a break between each drop. Consequently each drop can be treated independently. In our case however the growth of the produce is continual and is therefore treated all at once. It follows then that if in the case of yayin nesech, it was poured as a continual stream than the law would be similar to our case.3
The Ramban (Bava Batra 2a) presents a different answer. In the case of yayin nesech, issur is falling into heter. Therefore the heter annuls each drop of issur. In our case however, the vines and produce are each independently mutar. Similarly, he explains, the growth of the produce is also heter. Heter cannot annul heter. It is only once it reaches a measure of one two-hundredth that the issur is born and by that time it is too late.4
1 There is a debate regarding how this measure is calculated. See the Bartenura and Rosh for two opinions.
2 This topic, known as “rishon, rishon batel”, has a number of details, limits and exception (see Y.D. 134). For example, in some cases the batel parts can be “reawakened” – chozer ve’niur(see Y.D. 99:6). As always no practical halacha should be drawn from these articles.
3 The Ramban presents Rabeinu Tam’s answer slightly differently: In our case, the growth is happening by itself, whereas in the case of the yayin nesech, it is being poured by a person.
4 If it is not assur until it reaches one two-hundredth, how do we then explain the position of Rabbeinu Tam in the case where the fence was mended and then fell midway. The Ramban explains that the reason why it is batel after the first rebuilding is because he actively built the fence – bitul be’yadayim. Alternatively, the Ramban explains that there are those that argue with Rabbeinu Tam maintaining that in that case, each of the growth periods can combine to make the measure of one one-hundredth.
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