פירוש על תרומות 4:4

כדעתו של בעל הבית – because [he is one] who donates generously, and there are those who are miserly/with an evil eye, and there are those who donate the intermediate amount.

Introduction One can appoint a messenger (or agent) to separate terumah on his behalf. The question that our mishnah asks is, how much terumah should the messenger take out?

פיחת עשרה – and he donated one in forty.

One who says to his messenger: “Go and give terumah [for me],” he should give terumah in accordance with the mind of the owner. If the messenger knows how much terumah the owner of the produce usually gives, then he should give that amount.

או הוסיף עשרה – and donated [Terumah] from [one in] sixty.

If he does not know the mind of the owner, he gives according to the average amount one fiftieth. If he doesn’t know, then he should give an average amount.

תרומתו תרומה – for since that in one of he measures of he Sages he donated [Terumah], he can say to him: “For this I have estimated for you.”

If he gave ten parts less or more, the terumah is terumah. If he gave ten parts more or ten parts less, meaning he gave one fortieth or one sixtieth, it is still valid because these are all valid amounts of terumah.

ואם נתכוין להוסיף – that he knows the intention of the owner of the house, and he intended to add, even one, his heave-offering is not a heave-offering.

If, however, his intention was to add even one part more, his terumah is not terumah. However, if he knew how much the owner usually gives, and he intentionally added even one part or gave even one part less, then his actions are competely invalid. For instance, if the owner usually gave one fiftieth, and the messenger intentionally gave 1/51 or 1/49 his terumah is not terumah at all.