 According to Marcuse, Hegel, and Marx, human beings develop through a self-formative process wherein the external world (nature) is appropriated and transformed according to human needs. Labor is one of the main areas for this self-formative activity. The idea that labor is an essential part of a self-formative process is what distinguishes Marx from the classical economists such as Smith, Ricardo, etc. In classical economics, labor is simply the means by which individuals make provisions for themselves and their families. In these theories labor is not viewed as that activity by which the human subject is constituted. The Marxian view of labor as a self-formative process is what makes possible the Marxian theory of alienation and revolution.