Entail is a legal concept and set of associated rules restricting the manner in which real property (especially land) passes from one generation to the next; these rules tend to keep deceased estates together as a whole, and in the hands of a single owner (heir), rather than allowing them to be split up amongst multiple children (as would tend to happen in similar situations in Continental European law). Entail has been known in English law since feudal times, but it has of course evolved as the law has evolved. It is concerned with heirship, ensuring the male line and preserving intergenerationally its power and ownership of property. As Lawrence Stone has argued, a key element is psychological: a strong attachment by those involved to the principle of preferential male primogeniture.