The Sages taught this halakha, that a woman has a presumptive status of purity to her husband, only in a case where she does not have a menstrual cycle of days alone, but has a menstrual cycle that is determined both by fixed days and by physical actions she might perform, such as jumps. The reason is that since the matter is also dependent on a particular action, one can say that she did not jump and therefore she did not see blood, and consequently she is presumed to be pure. But with regard to a woman who has a menstrual cycle of days alone, and the projected day of her period arrived, it is prohibited for her to engage in intercourse with her husband.

The Gemara explains that Rav Huna maintains that the concern for impurity of women at the projected time of their periods applies by Torah law. Since she has an uncertain status of impurity by Torah law when the projected day of her period arrives, it is permitted for her to engage in intercourse with her husband only after an examination.

Rabba bar bar Ḥana says: Even if she has a menstrual cycle of days alone, she is permitted to her husband. Rabba bar bar Ḥana maintains that the concern for impurity of women at the projected time of their periods applies by rabbinic law. Consequently, she is not considered to have experienced bleeding, though by rabbinic law she should have examined herself to ascertain if she was pure.

Rav Shmuel says in the name of Rabbi Yoḥanan: With regard to a woman who has a fixed menstrual cycle, and her husband was away for seven days after the expected onset of her period, at which point he returned home, her husband calculates the days of her cycle; and if in the elapsed time it was possible for her to immerse and purify herself, he can presume that she did so, and he may engage in intercourse with her even without asking her whether she is pure.

Rav Shmuel bar Yeiva said to Rabbi Abba: Did Rabbi Yoḥanan state this ruling even with regard to a young girl, who is embarrassed to go and immerse herself, in which case one can claim that if her husband was away she would not have gone to the ritual bath?

Rabbi Abba said to Rav Shmuel bar Yeiva: Is that to say that Rabbi Yoḥanan applied this halakha to all cases? Did Rabbi Yoḥanan say that a woman who definitely saw blood is also permitted to her husband? You can say that Rabbi Yoḥanan said his ruling with regard to a case where it is uncertain whether the woman saw blood and it is uncertain whether she did not see blood, and therefore her husband may engage in intercourse with her, as one can reason as follows: If you say that she saw blood, one can still say that perhaps she immersed.

But if she definitely saw blood, it is not permitted for the husband to engage in intercourse with her. The reason is: Who is to say that she immersed? It is a conflict between an uncertainty as to whether or not she immersed, and a certainty that she saw blood, and there is a principle that an uncertainty does not override a certainty. In the case of a young girl, since it is uncertain whether she saw blood, and it is uncertain whether she immersed, she is permitted to her husband.

The Gemara raises a difficulty with this principle: And does an uncertainty not override a certainty? But isn’t it taught in a baraita: In the case of a ḥaver who died and left a storehouse filled with produce, even if the produce was there only that day, it has the presumptive status of produce that was ritually prepared, i.e., properly tithed. This is due to the presumption that the ḥaver tithed the produce himself or instructed others to do so. The Gemara infers: And here, the produce was definitely untithed at the outset, and there is uncertainty whether the ḥaver tithed it, and there is uncertainty whether he did not tithe it. And despite this conflict, the uncertainty whether it was tithed comes and overrides the certainty that it was untithed produce.

The Gemara rejects this claim: There, the conflict that leads to the question with regard to the produce’s status is between certainty and certainty, as the ḥaver certainly tithed the produce. This presumption is in accordance with the statement of Rav Ḥanina Ḥoza’a; as Rav Ḥanina Ḥoza’a said: There is a presumption with regard to a ḥaver that he does not release an item from his possession that is not ritually prepared.

And if you wish, say instead that in that case the conflict is between uncertainty and uncertainty, as it is possible that there was never an obligation to tithe this produce, in accordance with the opinion of Rabbi Oshaya. As Rabbi Oshaya said: A person can employ artifice to circumvent obligations incumbent upon him in dealing with his grain, and bring it into his courtyard in its chaff, so that his animal may eat from it, and this grain is exempt from tithe. Although the obligation to tithe produce applies even to animal fodder, it is permitted to feed one’s animal untithed produce that was brought into one’s home before being fully processed. Consequently, the case involving produce is a conflict between two uncertain factors, as it is uncertain whether or not the owner was obligated to tithe the produce in the first place, and even if he was required to do so, it is uncertain whether or not he tithed it.

The Gemara challenges: And still, is it correct that an uncertainty does not override a certainty? But isn’t it taught in a baraita: There was an incident involving the maidservant of a certain olive gatherer [massik] in the city of Rimon, who cast a non-viable newborn into a pit, and a priest came and looked into the pit to ascertain whether the baby was male or whether it was female, as the length of time of a woman’s ritual impurity after childbirth, even if she gave birth to a non-viable newborn, depends on whether the child was male or female (see Leviticus, chapter 12).

And the incident came before the Sages to rule whether or not the priest contracted ritual impurity while standing over the corpse, and they deemed him ritually pure. The basis for this ruling was: Due to the fact that martens and hyenas are common there, it is likely that the body was dragged away before the priest arrived at the pit.

The Gemara explains the challenge from this baraita: And here, where it is certain that the maidservant cast the non-viable newborn into the pit, and it is uncertain whether an animal dragged it away and it is uncertain whether no animal dragged it away, the Sages nevertheless ruled that an uncertainty comes and overrides a certainty.

The Gemara rejects this challenge: Do not say in the baraita that the woman certainly cast a non-viable newborn into a pit; rather, say