David Ausubel developed the theory of meaningful verbal learning based on the idea that learning occurs best when new information is related to what is already known. According to Ausubel, there are four processes of meaningful learning: derivative subsumption, correlative subsumption, superordinate learning, and combinatorial learning. An important instructional tool is the advance organizer, which strengthens a learner's cognitive structure by providing an overview of new material before it is presented in detail to help the learner incorporate the new information.