Pe'ah, Chapter 7, Mishnah 5. This mishnah deals with a process called "meidal ba'kerem," thinning out a vineyard. A meidal is someone whose vines are planted too close to one another, so that some of them must be uprooted in order for the remaining vines to grow properly and flourish. The word meidal comes from the root dalal, meaning to weaken and impoverish, except that here the weakening is done for the sake of strengthening the other vines.
The words of the mishnah and their meaning:
"HaMeidal b'gefanim" - one who performs this process. It is a form of pruning, except that pruning is done within the vine itself, whereas here entire vines are removed.
"K'shem she'meidal b'toch shelo" - just as he does this among the vines that belong to him.
"Ken hu meidal b'shel aniyim" - so too he may thin out among the vines that belong to the poor.
"Divrei Rabbi Yehudah" - this is the opinion of Rabbi Yehudah.
Which vines belong to the poor? Vines that were set aside as pe'ah, or vines made up entirely of olelos (defective clusters), which we mentioned in the previous mishnah, and which belong to the poor.
Rabbi Yehudah's reasoning:
The Yerushalmi first explains that the poor are considered partners, and just as a person performs this work in his field for himself, so he may perform it for his partner as well. In the end, however, the Yerushalmi rejects this line of reasoning.
The reason it concludes with: the thinning is a benefit to the poor, and because it is to their benefit, it is permitted to do it on their behalf.
Rabbi Meir's approach:
Rabbi Meir disagrees and says: "B'shelo hu rashai, v'ein rashai b'shel aniyim" - in his own vines he is permitted to thin out, but he is not permitted to do so in the vines that belong to the poor. Two reasons are given for his approach:
The poor prefer what they have in hand right now, and they are not interested in calculations of future improvement. They are not looking at the long-term gain; it may well be that their entire concern is the short-term gain.
Rabbi Meir views the poor person as a buyer. Just as when someone buys an object from you, you have no right to act upon his object, even if it is for his own good, so too with the poor person: you have no right to act upon what is his.
In summary: In this mishnah Rabbi Yehudah and Rabbi Meir disagree about the law of one who thins out a vineyard. According to Rabbi Yehudah, just as a person thins out in his own vines, so he thins out in those of the poor, because it is to their benefit (and not because of partnership, a reason the Yerushalmi rejected). According to Rabbi Meir, in his own he is permitted and in those of the poor he is not permitted, since the poor prefer the gain they have in hand right now, and according to a further explanation because the status of the poor person is that of a buyer, whose object one may not act upon even for his own good.