[2] On May 18, 2014, the English edition reached number one on The New York Times Best Seller list for best selling hardcover nonfiction[3] and became the greatest sales success ever of academic publisher Harvard University Press.

[12] In response to widespread curiosity abroad aroused by reviews of the original French edition published by Seuil in September 2013, it was translated rapidly into English and its publication date was pushed forward to March 2014 by Belknap.

It proved an overnight sensation[13] and ousted Michael Lewis's financial exposé, Flash Boys: Cracking the Money Code, from the top of the US best-seller list.

The book argues that there was a trend towards higher inequality that was reversed between 1930 and 1975 due to unique circumstances: the two world wars, the Great Depression, and a debt-fueled recession destroyed much wealth, particularly that owned by the elite.

[20] The book argues that the world today is returning towards "patrimonial capitalism", in which much of the economy is dominated by inherited wealth: the power of this economic class is increasing, threatening to create an oligarchy.

[21] Piketty cites novels by Honoré de Balzac, Jane Austen, and Henry James[20] to describe the rigid class structure based on accumulated capital that existed in England and France in the early 1800s.

[30] Krugman also wrote:[29] At a time when the concentration of wealth and income in the hands of a few has resurfaced as a central political issue, Piketty doesn't just offer invaluable documentation of what is happening, with unmatched historical depth.

"[31][32] British historian Andrew Hussey called the book "epic" and "groundbreaking" and argues that it proves "scientifically" that the Occupy movement was correct in its assertion that "capitalism isn't working".

[34] French historian and political scientist Emmanuel Todd called Capital in the Twenty-First Century a "masterpiece" and "a seminal book on the economic and social evolution of the planet".

He suggests it was "greeted with... erotic intensity" because of a demand for "scholarly respectability" that would affirm the belief that inequality is, quoting John Cassidy, "the defining issue of our era".

"[39] Icelandic professor Hannes H. Gissurarson asserts that Piketty is replacing American philosopher John Rawls as the essential thinker of the left.

Hannes admits that the "rapid rise in the income of the super-rich of the world" is happening but doesn't view this trend as being a problem so long as the poor do not get poorer.

The professors write that general laws, which is how they characterize Piketty's postulations, "are unhelpful as a guide to understand the past or predict the future because they ignore the central role of political and economic institutions in shaping the evolution of technology and the distribution of resources in a society".

[52] This idea is furthered by Matthew Rognlie, then a graduate student at M.I.T., who published a paper in March 2015 with the Brookings Institution that argues that Piketty did not take the effects of depreciation into account enough in his analysis of the growing importance of capital.

"[55] Marxist academic David Harvey, while praising the book for demolishing "the widely-held view that free market capitalism spreads the wealth around and that it is the great bulwark for the defense of individual liberties and freedoms," is largely critical of Piketty for, among other things, his "mistaken definition of capital", which Harvey describes as:[56] ... a process, not a thing ... a process of circulation in which money is used to make more money often, but not exclusively through the exploitation of labor power.

[60] Norwegian economist and journalist Maria Reinertsen compares the book to the 2014 book Counting on Marilyn Waring: New Advances in Feminist Economics, by Ailsa McKay and Margunn Bjørnholt, arguing that, "while Capital in the Twenty-First Century barely touches the boundaries of the discipline in its focus on the rich, Counting on Marilyn Waring challenges most limits of what economists should care about".

[61] On May 23, 2014, Chris Giles, economics editor of the Financial Times (FT), identified what he claims are "unexplained errors" in Piketty's data, in particular regarding wealth inequality increases since the 1970s.

The FT found mistakes and unexplained entries in his spreadsheets, similar to those which last year undermined the work on public debt and growth of Carmen Reinhart and Kenneth Rogoff.

The investigation undercuts this claim, indicating there is little evidence in Prof Piketty's original sources to bear out the thesis that an increasing share of total wealth is held by the richest few.

Piketty wrote a response defending his findings and arguing that subsequent studies (he links to Emmanuel Saez and Gabriel Zucman's March 2014 presentation, The Distribution of US Wealth, Capital Income and Returns since 1913) confirm his conclusions about increasing wealth inequality and actually show a greater increase in inequality for the United States than he does in his book.

[64] In an interview with Agence France-Presse, he accused the Financial Times of "dishonest criticism" and said that the paper "is being ridiculous because all of its contemporaries recognise that the biggest fortunes have grown faster".

Based on the information Mr Giles has provided so far, however, the analysis does not seem to support many of the allegations made by the FT, or the conclusion that the book's argument is wrong.

[65] In addition to Winship, the economists Alan Reynolds, Justin Wolfers, James Hamilton and Gabriel Zucman claim that FT's assertions go too far.

The values Piketty reported for the twentieth century (1910–2010) are based on more solid ground, but have the disadvantage of muting the marked rise of inequality during the Roaring Twenties and the decline associated with the Great Depression.