Rambam - 1 Chapter a Day

Based on Tosafot, Bava Batra 55b, the Kessef Mishneh explains the rationale for this ruling: The concept of impurity in the private domain is derived from the laws of a sotah. In that instance, the woman has a chazakah, an established status, of purity, and yet she is deemed impure because of the doubt. Hence, even if there are multiple doubts, the doubt will override the chazakah.

Which do not impart ritual impurity.

Which impart impurity when touched or when carried (Hilchot Tum’at Meit 2:9).

Which do not impart impurity (Chapter 1, Halachah 7).

A field in which there was a grave that had been plowed over.

Earth from either of these impart impurity according to Rabbinic Law (Hilchot Tum'at Meit 2:16).

If one holds a portion of his body over a human corpse, he contracts impurity due to the convention of ohel. This does not apply if he holds his body over an animal carcass.

See Chapter 19, Halachot 1-2, for more particulars concerning this situation.

Different laws apply with regard to the Paschal sacrifice (Hilchot Korban Pesach 6:11) and a nazirite (Hilchot Nizirut 9:18-19).

I.e., after he passed over the corpse, he became aware of its presence. The Rambam does not write that the person definitely touched the corpse, because it is possible that he swerved off the road and avoided it (Rav Yosef Corcus). For this reason, leniency is granted with regard to the situations mentioned in the previous note. Nevertheless, since this is unlikely, we are stringent with regard to terumah.

Even though the corpse it contained was dismembered (see Hilchot Tum’at Meit 4:7).

Even though he passed over a place in the grave in which there was no portion of the corpse.

Where we rule leniently in the public domain.

Similarly, he is impure if his body passed over the grave without touching it, because of tum’at ohel (Rav Yosef Corcus).

For we assume that they touched it.

Since an alley is a private domain, when a question of impurity arises there, we rule stringently [the Rambam’s Commentary to the Mishnah (Nidah 7:2)].

We do not say that sweeping the alley would have removed the carcass.

That indicates that it had been dead- and presumably in the alley- for a long time.

I.e., the carcass had not dried out, indicating it had died only recently.

Significantly, this ruling represents a reversal of the position taken by the Rambam in his Commentary to the Mishnah (ibid.).

I.e., saliva whose status was unknown, but was deemed impure, because it is possible that it was the saliva of a zav. See Chapter 13, Halachot 4 and 8.

Touching or moving the saliva of a zav would impart impurity.

I.e., it is neither burnt, as impure terumah would be, nor eaten, as pure terumah would be. Instead, its status is held in abeyance until it spoils or definitely contracts impurity.

Therefore the terumah is not consigned to fire as it would be were it to have certainly contracted impurity. Nevertheless, we also do not partake of it, lest it have contracted impurity.

I.e., not entirely dry, for in such an instance, the saliva would not impart impurity (Hilchot Metamei Mishkav UMoshav 2:1). Instead, we are speaking about saliva that is not moist enough to attach itself to a person who touches it [the Rambam's Commentary to the Mishnah (Taharot 4:6)].

Chapter 13, Halachah 13.

I.e., whether in the public domain or a private domain.

As stated in Chapter 13, Halachah 13.

I.e., impure because of zav impurity. If they are impure due to other factors, it is not significant in this context. As Rambam LeAm writes, it is highly unlikely for the majority of the members of a town to have contracted zav impurity.

For this is considered as a doubt that arose in a private domain. This applies even if he found the article on the day he lost it.
The Ra’avad [in his gloss to Halachah 10] differs and maintains that if it is found on the same day, it is pure, even in a private domain. The Kessef Mishneh justifies the Rambam’s ruling.

As in other instances when a doubt arises in a public domain.

For at night, a person is more likely to step on something without realizing it [the Rambam’s Commentary to the Mishnah (Taharot 8:3)]. Hence, there is a higher probability that an impure person touched the article.
There, the Rambam writes that if the article was lost in the public domain and left overnight, it is considered to have contracted midras impurity, but not the impurity associated with a human corpse. If it was lost in a private domain, it is considered to have contracted both forms of impurity. The Ra’avad mentions these concepts here.

Note a parallel in Hilchot Tum’at Meit 10:4.

I.e., a chavair, one who is careful about the laws of ritual purity and impurity. It is obvious that this is the intent, for everything in the home of an unlearned person is impure.
The article lost in the home of a chavair is pure, because it is unlikely that someone who is ritually impure will enter and touch articles there (Kessef Mishneh).

As is the rule regarding questions of impurity that arise in the public domain [the Rambam’s Commentary to the Mishnah (op. cit.)].

As is the rule regarding questions of impurity that arise in a private domain.
The Rambam does not mention treading on them, because it is assumed that since they were spread out, they would be noticed and would not have been trodden upon. A lost article, by contrast, is not obvious and may be trodden upon (Kessef Mishneh).

See Halachah 7.

Who will not know to restrain herself and is likely to spit anyway, even during the times she is in the nidah state. The Rambam and his source (Taharot 5:8) do not mention a man who is intellectually or emotionally compromised, because it is rare for a man to suffer from a zav condition. If, however, such a male is so affected, all of the saliva of unknown origin in a town would be considered impure.

Who was deemed as a zavah by Rabbinic Law. She is not likely to be concerned about where she spits and will do so carelessly. These laws also apply to a gentile male. The Rambam (and his source), however, do not mention a man so that the gender of the two subjects mentioned will be the same.

Even in the public domain. In his Commentary to the Mishnah (Taharot 5:8), the Rambam emphasizes that the intent is not that such saliva is considered impure because of the doubt- for if so, there would be no difference between this law and the law stated in Chapter 13, Halachah 4. Instead, we assume that the saliva is definitely impure. The rationale is that there is certainly one impure spot of saliva in the city. That saliva is considered as kevua, in a fixed place and we follow the principle, whenever there is an entity that is kevua, any entity that is found is considered to have the same status as it does.

The rationale is that it is suspected that she touched his clothes when the boat tipped (see Hilchot Metamei Mishkav UMoshav 9:4).

For we assume that if she was in an impure state, she would have taken care not to have imparted impurity to him.

Whether she is pure or impure. If she is impure, his garments are considered to have contracted impurity from her.

We do not suspect that an impure person touched his garments, as is the law regarding any doubt that arises in the public domain [see the Rambam’s Commentary to the Mishnah (Taharot 5:7)].

See Chapter 15, Halachot 6 and 10.

I.e., the person whom he touched at night.

Persons or utensils who touched him or were in the same building as he was.

This ruling applies even if he was taken to a public domain after he had been in a private domain and thus others would be deemed pure despite their contact with him.

This ruling applies even if he was taken to a public domain after he had been in a private domain and thus there were people already deemed impure because of contact with him [see the Rambam’s Commentary to the Mishnah (Taharot 6:1)].

Following the principle stated above: The status of all questions of ritual impurity depends on the situation at the time the matter is discovered.

And imparted impurity to it.

Even though the cistern has a border, as in the following clause, we assume that the oil made the border slippery and the saliva slid into the cistern from it.

I.e., even in a private domain.