Constitutional and absolute monarchies are similar because both have

A royal family is the common thing between the absolute and constitutional monarchies.

Explanation:

Absolute monarchy

In absolute monarchy the head of the state is supreme and possesses all the powers. The differences between the absolute and constitutional monarchies emerged during sixteenth and seventeenth centuries in Europe.  Absolute monarchy is also called undemocratic monarchy. in this the king or queen hold absolute power. They are responsible for all the economic and political decisions , they also aren't legally bound. they gain power through marriage or lineage. Brunei,Saudi Arabia and Oman are absolutist monarchy. Absolute monarchy emerged due to the decline of church powers and holy wars.

Constitutional monarchy

In constitutional monarchy the head of the state is elected monarch. Constitutional monarchies are also known as liberal monarchy and have limited powers because they rule with the parliament. The parliament is also responsible for the political and economic policies. constitutional monarch is legally bound. U.K, Canada, Australia and Jordan are constitutional monarchy.

the commander in chief