文獻所記秦國親屬法規以孝公時商鞅（約395-338 B.C.E.）變法之「民有二男以上不分異者，倍其賦」及「禁父子兄弟同室內息」二法令最重要，近年又見《嶽麓書院藏秦簡（伍）》出現始皇帝廿六年之「同父令」，「同父令」與前二者雖距一百五十年左右，但從家庭史的角度觀察，三者的發展脈絡清晰可見。從變法的角度看，推出法令必是要解決眼前的問題，商鞅變法提出的二法令，旨在消除當時秦國的「父子兄弟同室內息」之俗，其令「民有二男以上不分異者，倍其賦」之目的，是要鼓勵百姓在財產上進行分家，另再搭配官府的「名田宅」及「軍功授爵」制，讓家中男子在經濟上獨立而能自行脫離同室共居之俗。「禁父子兄弟同室內息」則直接限制居住空間，家中男性必須異居生活。二者看似無關，實則緊密相連。待至始皇時期，直接規定「同父」所生始能稱為兄弟姐妹，一夫一妻及一夫多配偶制的父系家庭從此獲得法律的保障，後夫及贅婿則落入社會貶抑之對象。 以「同父」為中心之家庭組織成為日後秦漢制定親屬法規的根本依據，族刑、置後、為戶、代戶、家產及爵位繼承之法條，都可就此種家庭組織找到其立法之原則。然其源頭至少可追溯到商鞅之變法。

The formation of the patrilineal family in the state of Qin was related with its laws. Three laws in particular were important. The first was promulgated in the sixth year of Duke Xiao (356 B.C.E.). Its main purpose was to encourage adult males to leave their birth family; otherwise they would pay double taxes. The second was announced six years later. It was a mandatory provision that forbid adult males from living together in the same house. The last was announced in the twenty-sixth year of the reign of the first emperor of the Qin dynasty (221 B.C.E.). It mandated that only people with the same father would be considered brothers and sisters, excluding those sharing a stepfather. These three laws are important for research on family history.
Although these three laws are separated by nearly one hundred and fifty years, their relationship is still close and the path of development is clear. In this study, the author uses Qin household registrations to discuss the composition of the family, showing how laws influenced the patrilineal family. After the Qin dynasty, the patrilineal family was generally considered an important principle in government legislation, including: family collateral punishments, status inheritance, distribution of property, and inheritance of household registration.