The book suggests that some 20th-century conventional wisdom was badly wrong. Inequality does not appear to ebb as economies mature, as Simon Kuznets, a Nobel-winning economist, argued in the 1950s. Neither should we expect the share of income flowing to capital to stay roughly constant over time: what another economist, Nicholas Kaldor, labelled a key fact of economic growth. Mr Piketty argues there is no reason to think that capitalism will “naturally” reverse rising inequality.
The centrepiece of Mr Piketty’s analysis is the ratio of an economy’s capital (or equivalently, its wealth) to its annual output. From 1700 until the first world war, the stock of wealth in Western Europe hovered at around 700% of national income. Over time the composition of wealth changed; agricultural land declined in importance while industrial capital—factories, machinery and intellectual property—gained prominence. Yet wealth held steady at a high level (see chart, first panel).