Liberty

In plain terms

Two things are called liberty and they pull apart.

The first is being left alone. You are free to the extent that nobody is stopping you - fewer obstacles, more liberty. On this view a state that does less leaves people freer.

The second is being able to determine your own life. Someone with no education, no money and no options is not free in any sense worth having, however few laws apply to them. On this view a state may have to do a great deal to make people free.

Berlin's warning was that the second can be turned: if freedom means being your real self, someone can claim to be freeing you by making you do what your real self would want. That argument was used to justify a great deal in the twentieth century, and it is the reason the distinction is worth keeping in view.

As a philosopher would put it

Berlin's negative liberty is the absence of interference by others; positive liberty is self-mastery, acting from one's own reason or real will. His argument is that positive conceptions are vulnerable to a slide in which an authority identifies a person's real interests and coerces them in the name of their own freedom.

The republican tradition offers a third conception. Pettit's non-domination holds that unfreedom consists in being subject to arbitrary power whether or not it is exercised - a slave with an indulgent master is unfree, though uninterfered with, because the master could interfere at will. That captures a range of cases neither of Berlin's concepts handles.

Mill's harm principle - that the only purpose for which power can rightfully be exercised over anyone against their will is to prevent harm to others - remains the standard liberal formulation, and its difficulty is that what counts as harm to others is where every dispute actually sits.

What is actually disputed

Whether positive liberty is a coherent political ideal.

Berlin's charge is that it licenses coercion in the name of the coerced person's real will, and the historical record supplies the examples. Defenders reply that the objection targets a metaphysical version - real self against empirical self - and that the ordinary claim, that freedom requires capacities and not merely the absence of obstacles, carries no such implication.

The republican conception complicates both. If unfreedom is domination rather than interference, then a law that removes arbitrary power increases freedom even though it interferes - which fits the intuitions about employment, marriage and colonial rule far better than either of Berlin's concepts.

What none of them settles is the harm principle's boundary. Almost everything a person does affects others somehow, and the work of deciding which effects count as harm has never been done by the principle itself.