הלכות שאר אבות הטומאה

Our Sages established five categories with regard to the ritual purity of clothes. They are the following:
a) The clothes of an unlearned person are considered as a midras, an article on which a zav had been supported, for people who partake of ordinary food in a state of purity. Similarly, the unlearned people themselves are considered as zavvim with regard to pure substances, as we explained.
b) The clothes of people who partake of ordinary food in a state of purity are considered as a midras for those who partake of the second tithe. The people who partake of ordinary food in a state of purity themselves - they are called perushim - are not considered as zavvim. Even with regard to terumah, a perush is considered pure, even if he touches terumah with his hands.
c) The clothes of people who partake of the second tithe are considered as a midras for those who partake of terumah.
d) The clothes of people who partake of terumah are considered as a midras for those who partake of consecrated food. The people who partake of terumah themselves are, however, not considered as zavvim with regard to consecrated articles.
e) The clothes of those who partake of consecrated foods are considered as a midras with regard to the offering of the red heifer, as explained in Hilchot Parah Adumah. A person who is pure with regard to consecrated foods is not considered as a zav with regard to the offering of the red heifer.

Similarly, our Sages established categories with regard to ritual immersion:
What is implied? If someone immersed himself without any intent, he is pure with regard to ordinary food, but he is forbidden to partake of the second tithe until he had the intent to immerse for the sake of the second tithe. If he immersed for the second tithe, he is assumed to be pure for the second tithe, but forbidden to partake of terumah. If he immersed for terumah, he is assumed to be pure for terumah, but forbidden to partake of consecrated foods. If he immersed for consecrated food, he is assumed to be pure for consecrated food, but forbidden to participate in the offering of the red heifer. If he immersed with the intent of participating in the offering of the red heifer, he is assumed to be pure for everything, for one who immerses for the sake of a more stringent circumstance is considered acceptable for a more lenient one.
If a person immersed without any intent, i.e., without thinking of any of these situations, he is pure only with regard to ordinary food and is considered impure as he was previously, even for the second tithe. Similarly, when a person washes his hands or immerses them, he must focus his attention, even if he desires only to partake of the second tithe. From that tithe and any level of sanctity higher, one must focus his intent. For ordinary food, however, it is not necessary for him to focus his intent.
All of these stringencies originate in Rabbinic Law. According to Scriptural Law, since the person immersed himself, he is pure with regard to all matters.

When a person who was pure with regard to terumah diverted his attention from partaking of it, the diversion of attention causes him to contract impurity. He is forbidden to partake of terumah until he immerses himself a second time. He need not, however, wait until nightfall.
If his hands were pure for terumah, but he diverted his attention from eating, even though he says: "I know that my hands did not contract impurity," his hands are impure because of his diversion of attention, for hands are busy. If this applies with regard to terumah, it can be inferred that the same principles apply with regard to consecrated food. Anyone who diverts his attention must immerse himself.
When a person did not guard himself from the impurity associated with a human corpse, if he is not certain that he did not contract impurity, he must have the ashes of the red heifer sprinkled on him on the third and seventh days after the doubt arouse, because of his diversion of attention. If he is certain that he did not contract the impurity associated with a corpse, but diverted his attention from other forms of impurity, he must immerse himself and wait until nightfall even for terumah. It is clear that all these immersions are Rabbinic safeguards.

Similarly, our Sages decreed that keilim that are discovered in marketplaces and streets - even in deserts - should be assumed to be impure, lest they have contracted impurity from a corpse or a zav. Similarly, saliva found in such places is considered to be impure, lest it be the saliva of a zav or the like.

All of the keilim found in Jerusalem are pure even if they were found on the way descending to a place of immersion. For the Sages did not institute a decree concerning keilim found in Jerusalem with the exception of knives for the slaughter of sacrificial animals. This was instituted because of the severity involving sacrificial animals.
When does the above stringency apply? To knives found in Jerusalem throughout the year. If, however, one finds a knife in Jerusalem on the fourteenth of Nisan, one may slaughter sacrificial animals with it immediately. This applies even if the fourteenth of Nisan fell on the Sabbath, for no decree was made with regard to knives found on that day. Similarly, if a knife was found on a festival, one may slaughter with it immediately. For it is assumed that all keilim are pure on the festivals.

If one found a knife on the thirteenth of Nisan, the ashes of the red heifer should be sprinkled on it, it should be immersed, and one may slaughter with it on the following day. For, on this day, our Sages considered it as if the thirteenth of Nisan was the seventh day of its purification with the ashes of the red heifer.

Our Sages decreed that any saliva of unknown origin found in the middle of the road in Jerusalem is impure like saliva of unknown origin found anywhere. Any saliva found on the side of the road in Jerusalem is pure, for the perushim walk on the sides so that they will not contract impurity through contact with unlearned people. During the festivals, the converse is true. Saliva in the middle of the road is pure, for all Israel are pure during the festivals. At the side of the road, it is impure. For there are few individuals who are impure during the festivals, and they move to the sides.

Just like a primary derivative of impurity creates a secondary derivative and a secondary derivative creates a tertiary derivative, when there is an unresolved doubt that an entity is a primary derivative it creates a secondary derivative of doubtful status, and a secondary derivative of doubtful status creates a tertiary derivative of doubtful status.

When there is a question whether terumah or consecrated food contracted impurity from a primary source of impurity of Scriptural origin - there is a question if the foods touched the impurity or not - they should be burnt because of this impurity.

There are situations where there is a question about a food's status for which the ruling is held in abeyance; they are not eaten, nor are they burnt. And there are other questionable situations that warrant the burning of terumah and, needless to say, consecrated foods.