Vygotsky's life goal was to create a psychology adequate for the investigation of consciousness. He stated that consciousness is constructed through a subject’s interactions with the world. Consciousness is neither reducible to behaviour nor separate from it, but instead is an attribute of the organisation of practical activity. It is the process that organises behaviour. Vygotsky introduced the idea of externally mediated activity that involves the use of external means to reach a goal. This led to the idea that mental processes could only be understood if we understand the tools and signs that mediate them. Wertsch believed that it was with this concept of mediation that Vygotsky made his most important and unique contribution (Wertsch, 1985).