KILAYIM (Heb. כִּלְאַיִם), the name of a tractate in the Mishnah, Tosefta and Jerusalem Talmud dealing with several biblical prohibitions of mixed species.
The Torah (Lev. 19:19; Deut. 22:9–11) lists a number of different examples of mixtures that are prohibited as mixed species. The halakhah reflected in the Mishnah and related works classifies the prohibitions under at least five categories: (1) interbreeding of animals (Ch. 8); (2) planting mixed seeds (Chs. 2 and 3), understood to include the grafting of trees (1:4, 7–8); (3) sha'atnez: mixing wool and linen in garments (Ch. 9); (4) planting grain or greens in a vineyard (Chs. 4–7); (5) ploughing or doing other work with two different species of animal (8:2–4). In its ten chapters, the Mishnah Kilayim deals with the regulations governing all five. In contrast to the assumption of the rabbinic halakhah, mixed seeds was not accepted as a separate biblical prohibition by some early traditions, who applied the relevant scriptural expression to the prohibition of grain in a vineyard. Although the kil'a'im laws themselves were derived from a relatively straightforward reading of the Torah, the details discussed in the tractate were deduced through the exercise of logic, analogies with other areas of law, or by application of the general rules to specific objects and situations. Jewish thinkers through the ages have speculated about the rationale for this prohibition, or have classified it as an unexplained or mysterious ordinance; however, the Mishnah and talmudic works deal with the technicalities of deriving and applying the law and not with its purpose.
Because the prohibitions only apply to the mixing of distinct species, but not to variants of a single species, Mishnah 1:1–6 deals with the botanical or biological classifications of seeds, trees or animals with a view to determining which are or are not separate species. There is evidence that the earlier stratum of halakhah, as represented by Beit Shammai, held to a stricter position that forbade even the mixing of sub-species (see Tosefta and Jerusalem Talmud 1:4). The rabbis' interpretations can be better understood when compared with ancient naturalists, as well as with the agricultural realia of Israel. Important contributions to the elucidation of kilayim from those perspectives have been made by I.E. Loew, S. Lieberman, and J. Feliks. On the whole, the halakhic classifications seem to owe more to popular usage and terminology than to scientific biology.
Questions dealt with in the Mishnah include the amount or proportion of the prohibited species that renders the field prohibited; separation of different species by visible barriers or distances (Ch. 3); procedures for changing a field over from one crop to another without leaving forbidden traces of the previous crop (3:6–7). Suggestions are offered on how to grow several species of greens of legumes in a small patch by separating them into distinct geometric patterns (3:1 etc.).
The prohibition of kilayim in the vineyard is spelled out very clearly in the Torah, along with the explicit penalty "lest the fruit of your seed which you have sown, and the fruit of your vineyard, be defiled"; hence it is treated more stringently, and the produce of such a mixture does not become permitted after the fact, as would occur in the case of mixed seeds.
The sages cited in the Mishnah Kilayim cover all the generations of tannaitic activity, from the days of the Temple (Eliezer ben Jacob) through to the scholars of Jabneh, Rabbi Akiva and his principal disciples. The Jerusalem Talmud, in addition to its commentary on the laws of the Mishnah and Tosefta, contains an aggadic digression (9:3, 32b) with biographical and hagiographical stories about Rabbi *Judah ha-Nasi and his contemporaries, material that was reworked in a less authentic version in tb, bm 83bff.).
J. Feliks, Ha-Ḥakla'ut be-Ereẓ Yisrael bi-Tekufat ha-Mishnah ve-ha-Talmud. (1963); idem, Kilei Zera'im ve-Harkavah: Masekhet Kilayim (1967); S. Friedman, " La-Aggadah ha-Historit ba-Talmud ha-Bavli," in: S. Friedman (ed.), S. Lieberman Memorial Volume (1993), 335, 11p.; I. Loew, Die Flore der Juden (1967); I. Mandelbaum, A History of the Mishnaic Law of Agriculture: Kilayim (1982); I. Mandelbaum, The Talmud of the Land of Israel: A Preliminary Translation and Explanation: Kilayim. Chicago Studies in the History of Judaism, eds. J. Neusner, W.S. Green, and C. Goldscheider (1990).
[Stephen G. Wald (2nd ed.)]