Elective Law

From Crusaderkings

Elective Law is designed mostly to replicate meritocratic or electoral forms of succession. The main use in-game is in merchant republics like Venice and Genoa, bishoprics and archbishoprics, and the Byzantine Emperor (at least initially).

In an Elective Law system, the strongest vassal (as measured by a composite of titles, prestige and personal characteristic scores) inherits the title. While this insures a string of better-than-average rulers, it's very dangerous from the standpoint of preserving dynastic power. Unless your dynasty has spread so far and wide that most of your vassals are also dynastic members (the Rurikovich clan in Russia is a good example).