I have studied about the each purpose of the two Encouragement Acts for the Marriage issued in 1724 and 1763 by tracing back to the Laws for the Military Houses ("Buke shohatto") restricting the range of social status of Daimyo's partner in life.
The Act of 1724 recognizes with some reservations that Daimyo takes a concubine as his wife, and the Act of 1763 permits the free remarriage though the first marriage is restrained strictly in the marriage range by "Buke shohatto".
The system of the hostage and "Sankin kotai" is the basic policy of Tokugawa Shogunate in order to control the Daimyos.
It seems that the Act of 1724 aims at reinforcing the hostage system, whereas shortening the stay in Edo under "Sankin kotai" system.
However, as a result of my research on the actual conditions, there are no documents or records showing that Daimyo actually took a concubine as his wife.
This means that in this period the institution of social position is more important than the new hostage system.
It seems that the purpose of the Act of 1763 is a relaxation of the restricted marriage range.
This supposition is supported practically by the investigation on the actual conditions of the marriages of Daimyos.
