Almost everyone agrees justice means giving people what they are due. The agreement dissolves the moment you ask what determines it. Is your due what you need, what you have earned, what you agreed to, what your effort merits, or simply whatever you acquired without violating anyone? Each answer produces a different society, and the shared definition conceals the entire dispute.
Ancient treatments framed the question differently from modern ones. Plato's Republic approaches justice as a kind of order: a just city is one in which each class performs its proper role, and a just person is one whose reason, spirit and appetite stand in the right relation. Aristotle gave the formula that has proved most durable — treat like cases alike, and unlike cases differently in proportion to relevant difference. It is genuinely useful and genuinely incomplete, since it hands the entire question to what counts as a relevant difference. Effort? Need? Talent? Birth? Each answer has been defended.
Modern theories concentrate on distribution. Rawls asks which principles people would choose to govern society if they did not know their own place in it — their class, talents, or conception of the good. He argues they would secure equal basic liberties first, then permit inequalities only where these attach to positions open to all and improve the position of the worst-off. The reasoning is that behind such a veil you would not gamble on landing at the bottom.
Nozick rejects the whole framing. Justice, he argues, is historical rather than patterned: a distribution is just if it arose through legitimate acquisition and voluntary transfer, regardless of the pattern it produces. His argument is that maintaining any pattern requires continuous interference with free choices — if people voluntarily pay to watch a gifted performer, the resulting inequality is unobjectionable, and undoing it means overriding choices nobody was wronged by. Critics respond that actual holdings descend from histories full of conquest and coercion, which by Nozick's own standard would demand enormous rectification.
Other traditions cut differently again. Utilitarians assess distributions by aggregate welfare, which can permit sacrificing some for the greater sum. The capability approach, associated with Sen and Nussbaum, asks not what resources people hold but what they are actually able to do and be — which reframes justice around real freedom rather than goods. And communitarian critics argue that all these theories abstract too far from the shared understandings that give justice its meaning in an actual community. None commands consensus, which is why this remains the liveliest area of political philosophy.