The doctrine encompasses entities such as humans, public areas, organs, citizenship, and prostitution, and is an exception to the general principle of freedom of contract.
[4] Res communes omnium were defined in the juristic Digest as things which "by natural law are the common property of all" and which therefore an individual could not appropriate.
The principle of things common to all is relevant to the concept of the res publica, "the sum of the rights and interests of the Roman people, populus Romanus, understood as a whole," from which the word "republic" derives.
In general, liberal legal systems assume that whenever the sides to a contract consent to its conditions freely and informed, with no coercion of any kind, then there's no justification to limit their agreements.
But even within the liberal approach, a departure from the freedom of contract principle can be warranted, as for lack of fairness or flawed consent.
For example, some liberals argue that prostitution should be prohibited because free trade cannot meaningfully issue from coercion or flawed consent.
Philosopher Michael Sandel argues that certain practices, such as organ trafficking or surrogacy, are intrinsically bad whether or not the people involved in them have freely consented.