“A hundred and fifty years proved the cure to be necessary but not sufficient.”
2015, Commemoration of the 150th Anniversary of the 13th Amendment (December 2015)
Context: At its heart, the question of slavery was never simply about civil rights. It was about the meaning of America, the kind of country we wanted to be –- whether this nation might fulfill the call of its birth: “We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable rights,” that among those are life and liberty and the pursuit of happiness. President Lincoln understood that if we were ever to fully realize that founding promise, it meant not just signing an Emancipation Proclamation, not just winning a war. It meant making the most powerful collective statement we can in our democracy: etching our values into our Constitution. He called it “a King’s cure for all the evils.” A hundred and fifty years proved the cure to be necessary but not sufficient. Progress proved halting, too often deferred. Newly freed slaves may have been liberated by the letter of the law, but their daily lives told another tale. They couldn’t vote. They couldn’t fill most occupations. They couldn’t protect themselves or their families from indignity or from violence. And so abolitionists and freedmen and women and radical Republicans kept cajoling and kept rabble-rousing, and within a few years of the war’s end at Appomattox, we passed two more amendments guaranteeing voting rights, birthright citizenship, equal protection under the law.
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44th President of the United States of America 1961Related quotes

Speech "The Tasks of Economic Executives" (4 February 1931) http://marx2mao.com/Stalin/TEE31.html Stalin said this in 1931, at the beginning of the rapid industrialization campaign. Ten years later, Nazi Germany invaded the Soviet Union.
Stalin's speeches, writings and authorised interviews
Source: Isle of the Dead (1969), Chapter 2 (pp. 58-59)

Où est le prince assez instruit pour savoir que depuis dix-sept cents ans la secte chrétienne n’a jamais fait que du mal?
Letters of Voltaire and Frederick the Great (New York: Brentano's, 1927), transl. Richard Aldington, letter 160 from Voltaire to Frederick II of Prussia, 6 April 1767 http://perso.orange.fr/dboudin/VOLTAIRE/45/1767/6824.html
Citas

As quoted in Biopolymers, Polyamides and Complex Proteinaceous Materials I (2003) by Stephen R. Fahnestock, Alexander Steinbüchel, p. 395
Attributed from posthumous publications

Source: Infinite in All Directions (1988), Ch. 3 : Manchester and Athens
Context: Fifty years ago Kurt Gödel... proved that the world of pure mathematics is inexhaustible. … I hope that the notion of a final statement of the laws of physics will prove as illusory as the notion of a formal decision process for all mathematics. If it should turn out that the whole of physical reality can be described by a finite set of equations, I would be disappointed, I would feel that the Creator had been uncharacteristically lacking in imagination.

Nobel lecture (1970)
Context: Our Twentieth Century has proved to be more cruel than preceding centuries, and the first fifty years have not erased all its horrors. Our world is rent asunder by those same old cave-age emotions of greed, envy, lack of control, mutual hostility which have picked up in passing respectable pseudonyms like class struggle, racial conflict, struggle of the masses, trade-union disputes. The primeval refusal to accept a compromise has been turned into a theoretical principle and is considered the virtue of orthodoxy. It demands millions of sacrifices in ceaseless civil wars, it drums into our souls that there is no such thing as unchanging, universal concepts of goodness and justice, that they are all fluctuating and inconstant. Therefore the rule — always do what's most profitable to your party. Any professional group no sooner sees a convenient opportunity to BREAK OFF A PIECE, even if it be unearned, even if it be superfluous, than it breaks it off there and then and no matter if the whole of society comes tumbling down.

Drucker (1993) Guru Guide. p. 293-294 as cited in: Nancy Campbell (2004) "The Practice of Management and the Idea of Leadership: An Overview of Theory and Practice"

Canto I, line 1277
Source: Hudibras, Part III (1678)