The most basic of post-Keynesian/Mandan themes is the production and distribution of social wealth. Social wealth is simply the accumulated output of society. A portion of this output is necessary to replace the commodities used up in that year's productive activities and a portion is necessary to maintain the population (e.g., food, clothing, housing, etc.). Whatever remains after these requirements are met is a surplus. This surplus, or net output, is then available for reinvestment and/ or for advancing the standard of living for some or all of the population. Post-Keynesian/Marxian economics endeavors to describe how the production of social wealth occurs, how it grows, and how it is distributed among various classes in society.