Second, as the example of the child suggests, changes in human behavior and consciousness, individual or collective, are mediated by other human beings through the use of tools (in the example: the chair, the child's cry, the father's pointing, etc.). No mind is self-sufficient. Activity systems are inherently social. Change occurs through the historically situated interactions of people and tools over time. As Leont'ev (1981) wrote, an activity system is not "an aggregate of reactions, but a system with its own structure, its own internal transformations, and its own development. ... If we removed human activity from the system of social relationships and social life, it would not exist and would have no structure" (pp. 46-47). Human activities are complex systems in constant change, interaction, and self-reorganization as humanbeings collaboratively adapt to and transform their environments through their actions with tools (including writing). Thus, consciousness is not individual but intersubjective, networks of systems mediated by our tools of interaction. Indeed, to paraphrase Robert Frost, human activity is social whether we work together or alone, for even the writer alone in a study is formed by and (potentially) forming the actions of others through the tool of writing. The solitary writer is part of some activity systems that give meaning and motive to individual acts of composition.