This declaration is valid for a Kohen or Levi, but as for a Yisrael, if he says the phrase for Terumas Maaser, he is separating it for something that is not his.

The reasoning of the order of the Mishnah is - if he would first separate Maaser and then Terumah, his separating Maaser precedes that of Terumah (which is prohibited); if he would first separate Terumah and then Maaser, he has either reduced or added to his Maaseros...

It would be like the Baraisa - one who reduces his Maaseros, his Maaseros are fixed but his fruits are ruined; one who adds to his Maaseros, his fruits are fixed but his Maaseros are ruined...

Baraisa (R. Yosi): He is relying on the stipulation of Beis Din, that one is permitted to deviate from 1/10th as much as a person could be mistaken.

What (else) is a stipulation of Beis Din? R. Yochanan said - that he fixes the Maaser Rishon on its northern side, Maaser Sheni on its southern side and Terumas Maaser on the northern (tip) of the northern side.

What (else) is a stipulation of Beis Din? When he will redeem, the Maaser Sheni added (by Beis Din's stipulation) will be redeemed.

This Mishnah's discussion only applies to liquids, but what if it was a solid? (Liquids become completely mixed, so it is true to say that when he takes the 10th, there is a mixture of Maaser and Chulin; but if the produce is a solid, it doesn't mix...)

If he had 100 figs, 50 large and 50 small, if he wants to take from the large ones for Maaser, he must take only 9 of them; and if he wants to take from the small ones, he must take 11. If he took 10 of the large ones, he has taken one too many and the stipulation of Beis Din applies, that one of them remains Chulin.

Question: Shouldn't there be a concern that when he then takes one of the 10 as Terumas Maaser, he has taken the one that is Chulin - and the pasuk states (Bamidbar 18:26), "the Terumah of Hash-m, Maaser from Maaser" - and not Chulin from Maaser...?

Answer (R. Bun bar Kahana): Rather, the stipulation of Beis Din that he makes is (that each of the figs should be 9/10th Maaser, and he should say), "The Maaser in which these fruits are obligated should be at the beginning of each stem.

Until this point, we have discussed only a large quantity of produce; but if it was a small quantity, for example, if he had 10 figs, 5 large and 5 small - if he takes from the large ones, he must take a little less than one for Maaser; if he takes from the small ones, he must take a little more than one. If he mistakenly took a whole large one, he has taken too much (and some of it is Chulin)...

Question: (As earlier) Shouldn't there be a concern that when he then takes a part as Terumas Maaser, he has taken the one that is Chulin - and the pasuk states (Bamidbar 18:26), "the Terumah of Hash-m, Maaser from Maaser" - and not Chulin from Maaser...?

Answer (R. Aba Kartigania): It is as if he said, "The Maaser in which these fruits are obligated is established at the beginning of the stem." And he ends by saying to the Kohen, "Until here (on the fig) I ended (the Terumas Maaser)."

(Note: According to the Vilna Gaon, this entire entry should not be part of the text, as it was already explained at the beginning of the Halacha.)