But Piketty does not lay heavy emphasis on such specifically economic answers to the question of why the present tendency of capitalism is alarming and requires correction. The centre of gravity of his belief that diverging levels of wealth are socially menacing is to be found in moral and prudential considerations. The moral concern is that such a world of material inequality would be ethically affronting. The prudential concern is that such a world would provoke social resentment on an intolerable scale, and that, in the resulting disorder, everyone would be worse off. Gross inequalities in the distribution of capital lead to "powerful political tensions, which are often difficult to reconcile with universal suffrage". If inherited wealth were to grow faster than output and income for a sustained period, then — so Piketty says — "the concentration of capital will attain extremely high levels-levels potentially incompatible with the meritocratic values and principles of social justice fundamental to modern democratic societies". It is hard, he says, to "imagine an economy and society that can continue functioning indefinitely with such extreme divergence between social groups".

Is that true? It doesn't seem that the capital-rich European societies of the period just before the First World War were socially unstable — quite the reverse. Piketty's forebodings seem to be that the social fabric will tear if disparities of private wealth become too large. That might be so were the same families just to become ever richer. But, with a few exceptions such as the Rothschilds, families seem not to be able to sustain a position at the apex of wealth for more than one or two generations. Another way of putting this is to note that aggregated statistics (which is what Piketty has assembled) can mask considerable volatility at the level of individual fortunes. The typical model extends over three generations: the entrepreneur accumulates a fortune, the managerial sons consolidate it, and the effete grandchildren, raised in conditions of affluence, dissipate it on cultural pursuits. The textbook literary illustration of this is Thomas Mann's Buddenbrooks (a novel not mentioned by Piketty, although absolutely on the subject of his book). A real-life example would be the wealth of the Gibbon family.  Gibbon's grandfather made a fortune as a government contractor and then as a director of the South Sea Company: at its peak it totalled some £160,000, a very considerable fortune in the early 18th century. When that fortune was confiscated in the wake of the bubble, he went on to make another fortune, almost as large. In the hands of Gibbon's father the family wealth gently subsided, but was still considerable.  The historian was able to maintain his literary and scholarly life on the remnants of his inherited wealth, but at his death his net worth was only in the region of £26,000. 

So it may be that r is greater than g, but the ability of children to burn through inherited wealth tends to be greater even than r. And even if later generations are not spendthrift, the process of inheritance will tend to divide family wealth into smaller piles, even in times of zero population growth. Over two generations under such conditions a family fortune will have been divided into four parts. Each of those parts will of course be larger than one quarter of the original fortune, as a result of the intervening years of return on the original capital. But unless marriage has introduced new sources of wealth into the family, each of the four parts will probably be less than the original fortune. Even the Rothschilds, though still exceptionally wealthy, are not today as comparatively wealthy as they were in the 19th century. This instability in the location of private wealth diffuses resentment at a social level, and also mitigates the moral point that Piketty levels at 21st-century capitalism.