The Mishnah (2:1) teaches that if a seah of produce has a rovah (a quarter) kav of another species mixed into it, then the quantity of foreign seeds must be reduced prior to planting. Given that the volume of a seah is equal to six kav the problematic threshold for mixed grains is one twenty-fourth. R’ Yossi however argues that if the threshold is crossed, all the foreign grains must be removed. The Bartenura explains that R’ Yossi understands that once one begins removing some foreign grains, leaving any would appear as though the owner was intentionally planting these mixed seeds. How do we understand the position of the Chachamim that if it is crossed, one simply needs to reduce the quantity of the foreign grain until it is less that one twenty-fourth?
The Bartenura explains that once the foreign seed is reduced below the threshold, it becomes batel – annulled. The Tosfot Yom Tov understands that in this case according to the Bartenura, on a biblical level, bitul takes affect at chad be’trei – when it is in the minority. However, the Chachamim forbad a mixture when it is one twenty-fourth due to marit ayin – the appearance that the owner is intentionally planting kilayim.
The Tosfot Yom Tov however finds this explanation difficult since we do not apply bitul if that which we wish to annul is discernible. The Tosfot Yom Tov therefore understands that the prohibition of kilayim only applies when one wish to plant the mixture. However, if the owner does not want the seeds that have been mixed in, then planting the mixture would not violate the prohibition on a biblical level. Nevertheless, due to concerns of marit ayin the Chachamim introduced this limit. This explains also why they allowed reducing the foreign seeds or even increasing the principle seed in order to reach the permissible proportion. Contrast this with the laws of bitul, where we find that one cannot deliberately force bitul. Indeed, the Yerushalmi explains that the measure of one twenty-fourth is due to marit ayin when explaining why one can deliberately alter the proportions to ensure the quantity of the foreign seed is below that level.
The Rambam (Kilayim 2:1) brings this rule, however he adds one further point – if one does not adjust the proportions to the permissible level and plants the mixture, he is punishable with lashes. The law is also stated in the Shulchan Aruch (YD 297:5). The Gra finds the addition difficult as it implies that a biblical rule has been violated. Yet we have already cited the Yerushalmi that since the mixture was not intentional, the concern is marit ayin, which is rabbinic.
The Imrei Bina (Pesach 10)1 answers that the Rambam agrees the prohibition at this level is rabbinic. However, this is only when one’s intention was not to plant the mixture. Once the Chachamim introduced the decree, albeit motivated by marit ayin, and one deliberately acts against it, it is now as if he intended to plant this mixture, which would be a biblical violation.
The Chazon Ish (Kilayim 4:12) however explains that when the Yerushalmi states that the issue is because of marit ayin it does not mean that the prohibition at these quantities is rabbinic because, as noted in the Rambam, even at these level it is prohibited on a biblical level. Rather the intention is that the Torah forbad any mixtures that appears as mixtures. Below that threshold, it does not appear as a mixture since planted grains generally have a small percentage of impurities. This provides a different understanding why there is no issue of trying to deliberately cause bitul. Simply put, the concept of bitul is not relevant to this case. We are not dealing with a prohibited quantity, but rather the appearance of a mixture. Consequently, our case would be no different to building a fence between a vineyard and a field of wheat, which is permitted. The Chazon Ish uses this explanation to defend the Bartenura against the attack of the Tosfot Yom Tov cited in the beginning of the article. In other words, the bitul referred to by the Bartenura is not in the standard sense of annulling the prohibited component, but rather it becomes not noticeable such that there is no issue of kilayim.
1 Cited in the Yalkut Biurim, Bava Batra 94a
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