Vygotsky viewed the ZPD as a better way to explain the relation between children's learning and cognitive development. Prior to the ZPD, the relation between learning and development could be boiled down to the following three major positions: 1) Development always precedes learning (e.g., constructivism): children first need to meet a particular maturation level before learning can occur; 2) Learning and development cannot be separated, but instead occur simultaneously (e.g., behaviorism): essentially, learning is development; and 3) learning and development are separate, but interactive processes (e.g., gestaltism): one process always prepares the other process, and vice versa. Vygotsky rejected these three major theories because he believed that learning should always precede development in the ZPD. According to Vygotsky, through the assistance of a more knowledgeable other, a child is able to learn skills or aspects of a skill that go beyond the child's actual developmental or maturational level. The lower limit of ZPD is the level of skill reached by the child working independently (also referred to as the child's developmental level). The upper limit is the level of potential skill that the child is able to reach with the assistance of a more capable instructor. In this sense, the ZPD provides a prospective view of cognitive development, as opposed to a retrospective view that characterizes development in terms of a child's independent capabilities. The advancement through and attainment of the upper limit of the ZPD is limited by the instructional and scaffolding related capabilities of the more knowledgeable other (MKO). The MKO is typically assumed to be an older, more experienced teacher or parent, but often can be a learner's peer or someone their junior. The MKO need not even be a person, it can be a machine or book, or other source of visual and/or audio input.