As indicated in the introduction, the problem with a predicate based module system lies in the difficulty to find the correct predicate from a Prolog term. The predicate `solution(Solution)' can exist in more than one module, but `assert(solution(4))' in some module is supposed to refer to the correct version of solution/1.
Various approaches are possible to solve this problem. One is to add an extra argument to all predicates (e.g. `assert(Module, Term)'). Another is to tag the term somehow to indicate which module is desired (e.g. `assert(Module:Term)'). Both approaches are not very attractive as they make the user responsible for chosing the correct module, inviting unclear programming by asserting in other modules. The predicate assert/1 is supposed to assert in the module it is called from and should do so without being told explicitely. For this reason, the notion context module has been introduced.