If a stranger comes to town and says that he is a priest, do we trust him? Do we give him our terumah, special foods apportioned to priests? Do we call him to the Torah first? Do we accept a priestly blessing from him?
The Gemara cites several earlier traditions that try to determine when, in the case that someone does not come from a known family, we actually can assume they are a priest. Let’s look at one of them, a beraita:
Presumptive status for priesthood is established in the land of Israel by the lifting of hands and distribution of terumah at the threshing floors. And in Syria and everyplace (outside Israel) that emissaries of the new moon arrive (representatives of the Jerusalem court who personally announce the date of a new month), the lifting of hands constitutes proof. But distribution of terumah at the threshing floors does not. And the status in Babylonia is like that in Syria.
According to this tradition, if we see someone go to the front of a synagogue to offer the priestly blessing, then we can trust that they are actually a priest. However, if they show up at the granaries to collect terumah, we only believe they are a priest in the land of Israel.
Why? The Gemara explains that this is because the mitzvah of terumah has the status of a biblical commandment in the land of Israel, and so everyone will be extra careful to do it correctly and only give it to legitimate priests. But in the diaspora, it has the status of a rabbinic command, and people will be less strict.
The Gemara adds a layer of nuance by distinguishing between two kinds of trust: trust for terumah, and trust for lineage. In the former case, we trust a stranger claiming to be a priest enough to give our terumah to them. In the latter, we also trust them enough to amend the family genealogical records to include their names.
The Talmud reads this beraita as referring only to the more limited trust: the kind where we give the priest terumah but do not change records. But this reading surprises some rabbis, who thought differently:
“What, not for lineage?” the Gemara answers, “No.”
So what’s going on? It seems to me that the author of the beraita thinks that we trust someone who is presumptively a priest not only to give them terumah, but to make a record of their priestly status and ensure it passes through their family line. But the later Babylonian rabbis are less sure, and are unwilling to change genealogical records on the basis of a presumption.
What I find particularly interesting about the Talmud’s discussion here is not how much it really does all come back to trust (what else can you do when genealogical websites and DNA tests are still 1,500 years in the future?) but how that trust is not necessarily in the person claiming to be a priest.
All of the actions described (collecting terumah, offering the priestly blessing) take place within a communal setting. While the presumptive priest is the one who receives the terumah, that’s only because a community has decided to treat this person as a priest and give him their terumah. And if the community doesn’t think that there is a priest in the synagogue, they just skip the priestly blessing. So in these cases, we have someone who the community accepts as a priest, and it is their collective trust that is under consideration here. The question isn’t: Does it look like a duck and quack like a duck? Instead, it’s: Do people treat it like a duck? Or, rather, a priest.
Read all of Ketubot 25 on Sefaria.