Mishnah 6. The previous mishnah dealt with a man who vowed not to benefit from his wife's handiwork, and so our mishnah too opens with one who takes a vow - this time a vow that touches on marital relations between husband and wife.
Why the husband cannot forbid her body to her:
A husband cannot forbid his wife to have marital relations with him, since through the marriage he is obligated to her, and he bears a prior duty to be available to her. Although a person may generally forbid by vow anything belonging to him to someone else, here, since there is a claim against him and he is already obligated, he has no halachic power to uproot that obligation.
Therefore the mishnah deals with a case in which he forbade himself from deriving benefit from her. This is a kind of indirect route: the Torah establishes that a person cannot forbid something in which another has ownership or a claim, and her body is not his to forbid; but he can forbid himself from deriving benefit from her body, and consequently he will no longer be able to have relations with her.
How long may this situation be allowed to continue?
The question is how long we wait before compelling him to divorce her and pay her kesubah. Two opinions are stated on this matter, and each one rests on a different source:
Two weeks - derived from a woman who gave birth to a girl, who is forbidden for two weeks.
One week - derived from a niddah, whose status by Torah law lasts only seven days.
At the end of the period, if he has not annulled his vow, he must divorce his wife and pay her kesubah.
Leaving home to learn Torah and to work:
From here the mishnah moves on to discuss how long a husband may refrain from the mitzvah of onah because he has left home:
Torah students - may leave to learn Torah in another city or another place, even without their wives' permission, for thirty days.
Laborers - who leave to work away from home, are limited to one week only.
The schedule of onah:
Now the mishnah lists the times of the mitzvah of onah stated in the Torah, according to the various occupations and how long they keep a man away from home:
"HaTayalin" - men of leisure who bear no particular responsibilities, and who are therefore obligated in onah every day.
"HaPoalim" - laborers, twice a week.
"HaChamarim" - donkey drivers, who travel for set periods, once a week.
"HaGamalim" - camel drivers, who go on longer journeys, once every thirty days.
"HaSapanim" - sailors, who are away for the longest stretches, once every six months.
These words are the opinion of Rabbi Eliezer.
The Gemara clarifies, however, that in practice the halachah regarding Torah scholars does not follow our mishnah; rather, they may leave to learn Torah even without their wives' permission for two years and even three years.