By: Rabbi Ari Enkin
While it is certainly important for one to establish whether one is a Kohen, Levi, or Yisrael, it is especially crucial that Kohanim are positive of their status. In our day, it is only Kohanim whose role is still required in order to discharge certain Biblical rituals and obligations. One such example is the Pidyon Haben ceremony. One who is under the impression that he is a Kohen, and officiates at a Pidyon Haben in that capacity, would render the ceremony completely invalid should there be any blemish on his lineage, even unknowingly. Likewise, one who is truly a Kohen, though for whatever reason is under the impression that he is a Levi or Yisrael, would be unintentionally violating many Biblical prohibitions every time he attends a funeral or enters a cemetery.
With the importance and centrality of lineage in ritual matters, one is compelled to question how we can be so certain that after so many centuries in Exile the chain of lineage has been properly maintained. Can anyone who claims to be a Kohen simply be relied upon?
Indeed, a number of authorities rule that the tribal designations in use today are merely “assumptions” with no halachic or scientific certainty as to their accuracy. It is actually presumed that most Kohanim today are likely not of pure lineage. In fact, already in the late Biblical era, and certainly in the Talmudic era, there was considerable doubt as to who was truly a Kohen. Because we are not sure who is truly a Kohen, there are several mitzvot which are no longer performed today in their entirety such a ma’aser, teruma, and challa. Similarly, a number of authorities rule that Kohanim today are not entitled to all the rights and honors that Kohanim had commanded in Biblical times.
The only way for a person to be halachically certified as a Kohen is if two witnesses were to testify that he and his father are unquestionably Kohanim and that they descend from those who are known to have served in the Beit Hamikdash. So too, in ancient times every family would posses and transmit to their children extensive documentation attesting to their status. Obviously, these things are simply not possible in our day.
In fact, the practice of honoring the Kohen with the first Aliya at every Torah reading, and similar honors afforded to Kohanim, is merely a custom in order to keep the ancient tradition alive. Indeed, a father is encouraged to redeem his firstborn son from as many Kohanim as possible, lest the Kohen who officiated at the Pidyon Haben was not of pure lineage. Nevertheless, there are a number of authorities who maintain that those who claim to be Kohanim based on family tradition are to be accepted as authentic Kohanim, without exception.
No matter what the actual status of Kohanim is today universal practice is to award the first Aliya of every Torah reading to anyone who claims to be a Kohen. So too, one who claims to be a Kohen is permitted to perform the Birkat Kohanim in the synagogue. One who has conducted himself all his life as a Kohen is not permitted to later claim that he was mistaken and is actually not a Kohen. One who does so would be suspected of ulterior motives such as a desire to marry a convert, divorcee, or the like. One who was raised in a completely assimilated or unobservant family should not necessarily conduct himself as a Kohen even if his father should tell him that he is one. One should seek rabbinic guidance in such a situation.
 Rivash 94; Maharashdam, EH 235.  Nechemia 7:63-64; Ketubot 24b.  Darkei Moshe, OC 457:4.  Rambam, Hilchot Issurei Biah 20:1-4.  Tur, EH 6:3; Perisha, EH 6:6; Middot 4:8; Sifri, Devarim 17:18.  Rashi, Bamidbar 18:1.  Maharashdam, EH 235.  Sheilat Yaavetz 1:155; Pitchei Tehsuva, YD 305:12.  Be’er Heitev, EH 6; Chatam Sofer, YD 336; Knesset Yechezkel 56.  Rema, EH 3:1.  Maharit 1:147.  Igrot Moshe, EH 4:11; Beit Avi 5:134.