无知之幕（veil of ignorance）和原初状态是约翰·夏仙义提出的概念，之后约翰·罗尔斯在《正义论》中使用。 是一种对特定道德问题判断的方法，过程是做以下思想实验：设想在“原初状态”下的一方，他们对自己所拥有的技能、品味、和地位于当社会的情况一概不知。而于此状况下让他们对权力、地位、和社会资源通过一定的原则分配予诸人。比如说，一个假定的奴隶制社会当中有50%的奴隶，于是做“无知之幕”思想实验的人们将会基于“进入这个社会的50%的人将会是奴隶”来做出选择，而不会只去认为自己是自由民。正如罗尔斯写道「…这一点保证了任何人都不会在选择原则时由于天然机会的结果或社会环境中的偶然事件而有利或不利。」这个概念是为了在分配社会合作的原则正义与否时抹除一己之私，或是自我阶层的私利而创造的。

The "veil of ignorance", along with the original position, is a method of determining the morality of a certain issue (e.g., slavery) based upon the following thought experiment: parties to the original position know nothing about their particular abilities, tastes, and position within the social order of society. When such parties are selecting the principles for distribution of rights, positions, and resources in the society they will live in, the veil of ignorance prevents them from knowing about who they will be in that society. For example, for a proposed society in which 50% of the population is kept in slavery, it follows that on entering the new society there is a 50% likelihood that the participant would be a slave. The idea is that parties subject to the veil of ignorance will make choices based upon moral considerations, since they will not be able to make choices based on self- or class-interest.