The unity theory derived from the English common law doctrine of coverture. A married woman had no right to hold property or to refuse her husband access to her body because upon marriage her person had merged legally into his and belonged to him. Sir William Blackstone, in his highly influential Commentaries of 1765 on “The Rights of Persons,” wrote:

"By marriage the husband and wife are one person in law; that is, the very being or legal existence of the woman is suspended during the marriage, or at least is incorporated and consolidated into that of the husband: under whose wing, protection and cover, she performs everything…and her condition during her marriage is called her coverture."

— Blackstone, Commentaries, Book I (1765) at 430.

Under the unity theory, charging a man with raping his wife would be equivalent to charging him with raping himself, a conceptual absurdity.

Blackstone further undermined married women's personhood, bodily integrity and safety with his comments on a husband's right to assault his wife physically in the name of “correction.” According to Blackstone's Commentaries, if a wife resisted her husband's authority he could:

"...give his wife moderate correction, for as he is to answer for her misbehavior, the law thought it reasonable to instruct him with the power of restraining her, by domestic chastisement, in the same moderation that a man is allowed to correct his apprentice or children."

— Blackstone, Commentaries, Book I (1765) at 442.