Similarly, with regard to awareness of ritual impurity, there are two cases that comprise four. It is prohibited for one who is ritually impure to enter the Temple or to consume a consecrated item. However, one who unwittingly violates this serious prohibition is obligated to bring a sacrifice for his transgression only if he was clearly aware of his ritually impure status both before committing the transgression and thereafter. The two cases of unwitting transgression in this area are: One who was aware and then forgot that he is ritually impure, and then either ate consecrated meat or entered the Temple, and subsequently recalled that he was ritually impure. Two additional cases are: One who was aware of his ritually impure status but was unaware that the food he was about to eat was consecrated and ate it, or he was unaware that he was about to enter the Temple and entered it.

Signs of affliction by leprosy are two that comprise four. The Torah (Leviticus 13) mentions two types of signs of affliction with regard to leprosy, baheret and se’et. Two additional, secondary signs of affliction were added. They are not as white as those delineated in the Torah. Consequently, there are derivatives of both baheret and se’et.

The mishna in Shevuot also mentions that the acts of carrying out on Shabbat are two basic actions that comprise four.

The Gemara asks: What is different here that our mishna teaches: Two that comprise four inside and two that comprise four outside, and what is different there, in tractate Shevuot, that the mishna teaches with regard to transfers on Shabbat: Two that comprise four, and nothing more?

The Gemara answers: Here, in tractate Shabbat, which contains the primary discussion of the halakhot of Shabbat, the mishna teaches the primary categories of labor that are prohibited on Shabbat, including carrying out from the private to the public domain, and it teaches the subcategories of labor that are prohibited on Shabbat, including carrying from the public into the private domain. But there, in tractate Shevuot, which does not contain the primary discussion of the halakhot of Shabbat, the mishna teaches the primary categories of labor prohibited on Shabbat but does not teach the subcategories of labor.

The Gemara asks: What are the primary categories of labor prohibited on Shabbat? They are acts of carrying out from the private domain to the public domain. However, the Gemara objects: The acts of carrying out are only two in number: There is the case of the homeowner who takes an object out of the private domain and places it in the hand of the poor person in the public domain and the case of a poor person who takes an object from the homeowner’s hand in the private domain and takes it out into the public domain. What are the two additional cases referred to by the phrase: Two that comprise four, in tractate Shevuot?

And if you say that the mishna in tractate Shevuot enumerates all four cases of carrying out, among them those for which there is liability and among them those for which there is exemption, including those mentioned in the second half of our mishna in which each individual performs only half of the prohibited labor, that is not feasible. The mishna in Shevuot teaches the prohibition of carrying out on Shabbat parallel to the signs of affliction by leprosy. Just as there, with regard to leprosy, all four of them are cases for which there is liability, so too, here, with regard to Shabbat, all four of them are cases for which there is liability.

Rather, Rav Pappa said that the difference between the manner in which the halakha is cited in tractates Shevuot and Shabbat must be understood as follows: Here, where it contains the primary discussion of the halakhot of Shabbat, the mishna teaches both cases of liability and cases of exemption, meaning cases of carrying out for which one is liable by Torah law as well as those for which one is exempt by Torah law. However, there, where it does not contain the primary discussion of the halakhot of Shabbat, the mishna teaches cases of liability but does not teach cases of exemption.

The Gemara asks: What are the cases of liability? They are acts of carrying out from the private domain to the public domain. The Gemara objects on the grounds that there are only two acts of carrying out: Carrying out while standing inside and carrying out while standing outside. What is the meaning of the phrase in Shevuot: Which comprise four? The Gemara answers: It is possible to arrive at a total of four. Cases of carrying in from the public domain to the private domain are also enumerated in tractate Shevuot. Consequently, there are two cases of carrying out and two cases of carrying in.

The Gemara objects: In Shevuot, the phrase: Acts of carrying out, is taught in the mishna, not acts of carrying in. Rav Ashi said: The tanna in Shevuot also refers to carrying in as carrying out.

From where do I know this? From that which we learned in a mishna: One who carries out an object from one domain to another is liable. Are we not also dealing with a case where he is carrying it in from the public domain to the private domain, and nevertheless the mishna characterizes it as carrying out?

And what is the reason that the term carrying out is used to refer to an act of carrying in? The tanna characterizes any act that involves lifting of an object from its place and transferring it to another domain as carrying out. Carrying out does not refer only to carrying an object out from one’s house. Rather, it is a general depiction of moving an object from the domain in which it is located into another domain.

Ravina said: Our mishna is also precise, and its language leads us to the same conclusion, as the expression: Acts of carrying out on Shabbat, was taught in our mishna, yet immediately a case of carrying in is articulated. The first case listed in our mishna involves the poor person placing an object into the hand of the homeowner, which is a case of carrying in from the public to the private domain. The Gemara notes: Indeed, conclude from this that the term carrying out also refers to carrying in.

Rava said: The language of the mishnayot poses no difficulty. The tanna in both of these mishnayot did not teach: Acts of carrying out on Shabbat. Rather, he taught: Domains of Shabbat. The correct version of the mishna is: The domains of Shabbat are two that comprise four, and, according to this tanna, there are four instances of prohibited labor in these two domains, inside and outside.

Rav Mattana said to Abaye: The mishna speaks of two that comprise four inside and two that comprise four outside, for a total of eight. Yet there is a difficulty: Are these eight cases? They are twelve. Upon closer inspection, in the four cases in the latter part of the mishna, the homeowner and the poor person each performs an individual action contributing to the overall prohibited labor of carrying in or carrying out. Consequently, there are four actions in the first part of the mishna and eight actions in the second part.

Abaye responded: According to your reasoning, they are sixteen actions, as even in the first part of our mishna, the one who receives the object and the one who places the object each participates in the performance of a prohibited action. Therefore, there are a total of sixteen actions.

Rav Mattana said to Abaye: That is not difficult, as granted,