There is a huge amount to admire and welcome in this book. In the first place, it is impossible not to warm to Piketty's scorn for the mathematical turn in economics, which he skewers pitilessly as a chosen rhetoric, rather than an instrument of inquiry or analysis:

. . . the discipline of economics has yet to get over its childish passion for mathematics and for purely theoretical and often highly ideological speculation, at the expense of historical research and collaboration with the other social sciences. . . . This obsession with mathematics is an easy way of acquiring the appearance of scientificity without having to answer the far more complex questions posed by the world we live in.  

As if to underline his impatience with the mathematical mode of economics, Piketty refers to his book as a work of history, and he illustrates his points by using literary examples. Piketty is of course aware that novels are not data. His references to Austen and Balzac are really just grace notes, although they do signal his admirable desire to move economics away from barren technicalities and back towards what it was in the hands of David Hume and Adam Smith, that is to say part of the intellectual interests of a normal educated person.

Second, Piketty's assiduity in collecting data and thus putting the argument on an entirely new and more secure evidential footing, even though it is inevitably the product of collaboration (which Piketty generously and scrupulously acknowledges), is deeply impressive. That labour of data collection unfolds its implications in two directions. On the one hand, it shifts the point of discussion away from theory and towards fact — always a helpful move. On the other, it validates Piketty's bona fides as a public intellectual. At a number of points in this study Piketty states that his purpose is to stimulate a well-informed debate on the trajectories of global wealth accumulation and the policy options which should respond to it. As he says in his conclusion, "all of my conclusions are by nature tenuous and deserve to be questioned and debated. It is not the purpose of social science research to produce mathematical certainties that can substitute for open, democratic debate in which all shades of opinion are represented." More writers make these kind of statements than actually mean them, but in Piketty's case they are transparently sincere, and his labour of data collection vindicates them, as does his eschewal of polemical narcissism.

Assuming Piketty is right in his diagnosis that the world is moving towards something like the economic state it was in just before the First World War, in which capital had reached very high and increasing levels, one might ask the question: What would be wrong with such a world? Why does it require correction by means of public policy?

Piketty has a number of answers. In some ways the most interesting is one derived from American experience in the early years of the present century. In the years leading up to the crash of 2007-8, Piketty suggests, growing income inequality led directly to financial instability. The mechanism for this was that those on lower incomes were induced to take out loans they could not afford to boost their standard of living.