Chapter 13 focuses on the accessio and confusio doctrines, traditionally sibling doctrines to the specificatio doctrine. The accessio doctrine includes three types of combinations: immovables and immovables, movables and movables, and movables and immovables. Confusio concerns only mixture of movables. The big picture of these doctrines is that there is little sign of convergence, except perhaps in confusio. From an economic standpoint, it is quite clear when two things should be considered combined (thus the accessio doctrine applies) rather than separable: If (the value of attached thing) > (the value of the two post-separation things combined) + (the cost of separation), the two things should remain combined. The next question is who should own it. The key concern behind my analysis is still to deter opportunistic or careless interference with other’s property.