Presumption of priestly descent

In Judaism, the presumption of priestly descent is the presumption that a Jewish man is a priest (kohen), based not on genealogical records of descent from Aaron or on Jewish court rulings, but rather by observation of his priestly behavior as recognized by his peers and community. Such an individual is called a kohen muhzak (presumed kohen or status-quo kohen; כהן מוחזק, from חזק). The criteria for this determination are defined in rabbinical halakhic texts. In the Land of Israel the criteria consisted of performing the Priestly Blessing and receiving terumah at the threshing floor, while in Syria and Babylonia the Priestly Blessing constituted adequate grounds without receiving terumah. Other criteria might include observing the priestly laws about impurity and forbidden marriages, or receiving the first aliyah in synagogue. Rabbi Jose ben Halafta extolled the soundness of the this "presumption" (chazakah) by calling it a basis for the entire halakhic concept of chazakah. It is based on this presumption that all poskim agree to forbid presumptive kohanim from marrying a divorcee. Among the Acharonim, this presumption described as "a sound presumption". The later books of the Bible describe the use of lineage documents to prove priestly descent, along with other recordings of lineage. The Talmud gives little information regarding the content and form of the lineage document, in contrast to other Rabbinic documents that are described in greater length (for example the Ketubah, Get, business documents (Shtarei Kinyan), and the document of freedom for a bondsman (Shtar Shichrur)). Rashi mentions that when the Israelites were required to ascertain their lineage to join their respective tribe, this document was brought in tandem with the testimony of witnesses. Yair Bacharach noted that the lineage document was not commonly used by kohanim. He argues that the testimony of two Kosher witnesses regarding a kohen's lineage makes him eligible for service. Similarly, the Tur states that two witnesses are sufficient to qualify a kohen for service on the Mizbeach.