Maasrot, Chapter Two, Mishnah One
This mishnah deals with someone who gets produce from someone else while walking on the street. There are two questions here: 1) can he eat them without tithing? 2) What if they were already tithed?
1) If one was passing through the street, and said Take for yourself from my figs, one may eat them and be exempt from tithes.
a) Therefore if they brought them into their houses, they must separate [tithes and terumah] as if they were certainly untithed.
2) [If he said], Take and bring it into your houses, they may not make a chance meal of them.
a) Therefore if they brought them into their houses, they need tithe them only as demai.
Section one: The mishnah deals with a person who is bringing figs into his home and offers some to someone else. One can assume that they have not been tithed because usually produce that one is not bringing to market is not tithed until one brings it home. Had the figs already been tithed, he would have told the person he was giving them to that he could eat them at home. The receiver can eat the figs without tithing them before he brings them home, but once he brings them into his house he must tithe them before he can eat them. The tithes that he separates have to be considered certain tithes because we can be quite certain that they were not yet tithed.
Section two: In this case, the person told him that he can eat the figs in their own home. This is taken as a hint at two possible things. First of all, he may be saying that the figs have already been in his home, which would make them liable for tithes, but they have not yet been tithed. Therefore, it is forbidden to make a chance meal of them before he tithes them. The other possibility is that he is telling him that he can eat them even in his own home because they have already been tithed. Therefore, when he brings them into his home he must tithe them as if they are demaidoubtfully tithed produce. In sum, the mishnah is concerned for two opposite problemswhile in the street he cant eat them lest they already were brought into the original persons house and they were not tithed; once he brings them home, he must be concerned lest they already were tithed and therefore, the tithes that he takes out have the status of demai and not certain tithes.