Categories of Forbidden Relations
סוגי העריות
Many mitzvot deal with the family and with the prohibitions of gilui arayot (forbidden sexual relations). The Rambam lists thirty-six Torah mitzvot in Hilkhot Issurei Bi'ah, and together with the mitzvot dealing with the punishments for those who transgress gilui arayot deliberately, after being warned and before witnesses, there are about fifty mitzvot. Even the upright among the nations of the world have accepted upon themselves the general Torah principles of the prohibitions of arayot, as they are commanded according to the seven Noahide laws.
There are four categories of forbidden relations. The first includes each person's own relatives, such as his mother, sister, daughter, aunt, brother's wife and father's wife. When a person marries, a second category of arayot is added, which includes his wife's relatives, such as her mother, sister and daughter. Of course, this prohibition applies correspondingly to the woman, once she marries, with regard to her husband's relatives. The third category includes only a single definition, but in practice most women are included in it: the prohibition of eshet ish (a married woman). From the moment a woman marries her husband, this prohibition applies with regard to all other men in the world. The fourth category includes two prohibitions that amount to a change in the order of the world: one is the prohibition of male homosexual relations (explained in Peninei Halakha: Simḥat Ha-bayit U-virkhato 4:13-17), and the second is relations between a human being and another species, such as a domestic animal, wild animal or bird.
A child born of gilui arayot has the status of a mamzer (explained below in sections 8-10).
A less severe level is having marital relations with a woman who is a nidda, that is, during her period, as long as she has not become pure by immersing in a mikveh. However, since these relations do not involve the betrayal of a married woman or incest within the family, the severity of this prohibition is less than that of the other prohibitions of adultery, and if a child is born of them, he is not a mamzer.
A lesser level is the prohibition of having marital relations with a woman who is not married, whether single, widowed or divorced, for it is permitted to have marital relations only within the framework of marriage. If she is also a nidda, an additional, more severe prohibition is added. In any case, since these relations do not involve the betrayal of a married woman or incest within the family, if a child is born of these relations, he has no blemish.
There is an additional prohibition for a man: to emit seed in vain, since by doing so he squanders this power, which is meant to increase joy and love between him and his wife, on a passing desire. The poskim disagree whether this prohibition is from the Torah or rabbinic (Peninei Halakha: Simḥat Ha-bayit U-virkhato 4:1, n. 1).