For example, Trobriand Islanders prohibit both sexual relations between a woman and her brother, and between a woman and her father, but they describe these prohibitions in very different ways: relations between a woman and her brother fall within the category of forbidden relations among members of the same clan; relations between a woman and her father do not. This is because the Trobrianders are matrilineal; children belong to the clan of their mother and not of their father. Thus, sexual relations between a man and his mother's sister (and mother's sister's daughter) are also considered incestuous, but relations between a man and his father's sister are not. A man and his father's sister will often have a flirtatious relationship, and, far from being taboo, Trobriand society encourages a man and his father's sister or the daughter of his father's sister to have sexual relations or marry.