(Lomdus alert: this question is not for beginners.)

In Maseches Demai (5:10-11) we learn that taking teruma from a vadai (=untithed produce) on demai (=possibly untithed produce) does not work, even on the vadai itself.

I totally don't understand why this should be. Either way: if the demai was not tithed, then they are both untithed, so the teruma should be good. And if the demai was tithed, then it turns out he just took extra-large teruma from the vadai. What's the problem, that the mishna requires him to take teruma again?

  • Demai is assumed to have teruma gedola seperated already because even amei haaretz do that
    – Double AA
    Jun 19, 2013 at 19:59

1 Answer 1


If I'm reading the Mishna right, the case of ודאי על הדמאי means you take some real Tevel Maaser Rishon and declare it all Terumat Maaser for the Maaser Rishon you separate from the Demai. If the Demai needs it, then such a declaration works and the real Tevel Maaser Rishon is now real Terumat Maaser. If the Demai doesn't need it, then the real Tevel Maaser Rishon remains real Tevel Maaser Rishon because it wasn't being used for anything. (Note one cannot declare an entire crop Teruma even if one tried.) Thus if it is still real Tevel Maaser Rishon, it still needs to have Terumat Maaser seperated from it.

  • I don't see how you can read that he took the entire vadai and made it teruma for the demai. Then the mishna (or Kehati at least!) should have denoted somehow that the reason it does not work is because of that technicality that you can't declare an entire crop as teruma. According to what you're saying, if he only took part of the vadai as teruma it should be good - but that's not what the mishna says. In several places Kehati states that מעשר מן החייב על הפטור is ineffective, in general, not just when you exhaust the חייב. Why is that?
    – Shaul Behr
    Jun 20, 2013 at 7:59
  • You seem to think the case is מעשר מן הודאי על הדמאי והודאי. Not sure why you think that. Even if there is more vadai around, you aren't seperating for it.
    – Double AA
    Jun 20, 2013 at 8:21
  • 1
    As for your question about chiyuv on petur, it's a mishna terumot 1:5. I don't know what is so surprising about that rule.
    – Double AA
    Jun 20, 2013 at 9:46
  • Ah, I hadn't got to Terumos yet, so I didn't know that mishna. :) But it just pushes the question to there. Why can't you take teruma from chayav on patur?
    – Shaul Behr
    Jun 20, 2013 at 9:50
  • Because the patur can't have teruma taken from it. It's not tevel. I'm not sure why you think otherwise.
    – Double AA
    Jun 20, 2013 at 13:56

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