Vygotsky (1965) moved beyond focussing upon the individual, construing and constructing meanings of reality, instead seeing individual learning as grounded in the socio-cultural context, and symbolically mediated through language/dialogue. For Vygotsky, the learner's social interactions, including those with teachers and other learners, are critically important to cognitive development, resulting in Vygotskian theory often being referred to as social constructivism. Vygotsky's Zone of Proximal Development (ZPD) describes how engagement with another (teacher or peer) enables learners to refine their thinking or performance and make it more effective; this idea was taken further by Bruner (1966) in developing the concept of scaffolding. Bruner (Ibid.) views education as a process of personal discovery, with cognitive growth occurring as students progress through three learning stages: enactive, iconic and symbolic. In order to generate understanding, students must move through the stages successively, generating new concepts and ideas in a process of discovery learning, or, with the assistance of another, through guided discovery. Knowles et al. (1998) contend that this discovery should take place in real-life situations in order to be truly effective and argue that much adult learning is informal. Knowles is best known for his proposal of a theory of adult learning which will now be reviewed.