Piketty and r > g

Thomas Piketty's Capital in the Twenty-First Century (2014) reframed the academic and public discussion of inequality by providing both a century of international comparative data and a theoretical account of why rising inequality might be the norm rather than the exception in capitalist economies. His central argument, compressed into the formula r > g, is straightforward: when the rate of return on capital (r) exceeds the rate of economic growth (g), wealth concentrates. Those who hold capital accumulate faster than the economy as a whole grows, which means their share of total wealth rises continuously.

Piketty's historical data showed that r > g has been the normal condition for capitalist economies over the past two centuries, with the notable exception of the period roughly 1914-1970 -- when wars, depression, and high progressive taxation dramatically reduced the value of existing capital and redistributed income. The mid-century compression of inequality that many Americans experienced as normal was, in this analysis, an anomaly produced by exceptional historical circumstances rather than a sustainable equilibrium to which capitalism naturally tends.

The policy implication Piketty drew was an annual global wealth tax -- a direct tax on wealth holdings rather than income flows -- designed to prevent the indefinite accumulation that r > g implies. He acknowledged this was politically utopian but argued it was analytically necessary: income taxes alone, which miss unrealized capital gains and can be minimized through legal restructuring, are insufficient to address wealth concentration that operates primarily through asset appreciation.

The history of the distribution of wealth has always been deeply political, and it cannot be reduced to purely economic mechanisms. It is shaped by the policies that societies choose to adopt.Thomas Piketty, Capital in the Twenty-First Century (2014)

Piketty's work was not without critics. Some economists disputed his data on historical rates of return, arguing that he had overestimated r by conflating capital with wealth and ignoring depreciation. Others argued that his projected future inequality was too mechanistic -- that political responses, technological change, or demographic shifts would prevent the indefinite rise in wealth concentration that his model implied. Lawrence Summers argued that secular stagnation -- chronically low growth -- might actually moderate r, reducing rather than increasing inequality over time.

Whatever the disputes about Piketty's specific projections, the core observation that wealth concentration has risen sharply since 1980, and that existing tax systems are poorly designed to address it, has held up well against scrutiny. The subsequent work of Saez, Zucman, Chetty, and others has provided more granular documentation of the concentration dynamic that Piketty described. The analytical disagreements are about mechanism and magnitude, not about whether the trend is real.