1945年,波普尔(Karl Popper, 1902 – 1994)发表《开放社会及其敌人》 ( The Open Society and Its Enemies) 一书,批评极权主义并替自由民主制度辩护,在西方知识界影响极大。这部著作与哈耶克的《自由宪章》(The Constitution of Liberty, 1960),伯林 ( Isaiah Berlin, 1909 – 1997) 的《自由四论》(Four Essays on Liberty, 1969),以及稍后的罗尔斯(John Rawls, 1921 – 2002)著名的《正义论》(A Theory of Justice, 1971)一起被公认为二十世纪自由主义的四大经典文献。
1. Each person is to have an equal right to the most extensive basic liberty compatible with similar liberty for others. (liberty principle)
2. Social and economic inequalities are to be arranged so that they are both: a) reasonably expected to be to everyone's advantage and b) attached to positions and offices open to all. ( difference principle)