There is no fully satisfying definition of liberty but we can clarify the issue by referring the issue of liberty to a set of 2 questions. The answer to these questions might not be as clear as those question for they may overlap. Confusion is in the answer, not in the question. Why ? Because questioning is an entirely intellectual process, which depends on our logical abilities, while the answer is in a matter of context, behavior, action which do not depend only on conceptual schemes.

 Negative freedom is in a way the most evident definition of liberty, it is the power to do whatever we want to do.
 Freedom is a political concept for it is when I am refrained by others form doing what I wish that I do not feel free.

An evident question is now : why should the others refrain me from doing what I wish. Interestingly enough, Berlin does not answer by « because I might be wrong », but more broadly, without judging the right or wrong of the wishes, because there is no « automatic harmony » between men (p. 123). We are back to the issue of pluralism and this is a twofold critique :

 Of Marxism (ultimately men, when they are not divided by the division of labor, will join in a universal community).
 But also of Mill’s liberalism (p. 126, and more broadly of « market liberalism » which induces a theory of « spontaneous order »).

The lack of harmony in Men’s prospects implies that sometimes liberty should be coerced, and legitimately so. But the crucial point is not to call liberty such a coercion (even a reasonable one). Also, that leads Berlin to say that there are sometimes things more important than liberty. How can coercion on liberty be legitimate ? As a practical compromise (p. 126). However, those things are not substitute for liberty. A striking argument is the argument about the Egyptian peasant for it amounts finally to an implicit racist assumption to think that the Egyptian peasant has a « different » idea of liberty ; that is a deep reflection about the ambiguity of nowadays’ « differencialism ».

Liberty is indeed ultimate an end, but it is not the sole « goal of men ».

In a way, that illustrates the power of tautologies (as Wittgenstein put it, the interest of tautologies is that they are always true…) : liberty is liberty, not equality, not even justice or truth (p. 128). It is not even just equal to democracy (p. 129) because, as in Hobbes, it may be compatible with authoritarianism. « Everything is what it is » (p. 125)

Negative freedom can be described as an « area » where none interferes with someone’s business. But liberty is also a modern concept, it also a « cultural era » so to say.

It is a modern doctrine : that does entail no relativism on Berlin’s part, who borrows Constant’s classical argument about the liberty of the Ancients and the liberty of the Moderns. It means that liberalism is a progressive doctrine, a doctrine that asserts that humanity is able to give new guaranties to fundamental human values. It should be noted that while the Ancients had indeed no formal protection of their privacy and individual rights it might well be because they did not need it rather because they lacked such an idea. Arendt no less classical thesis about the Ancients is that they had a social consensus about private life, and that consensus disappeared with the apparition of a middle term between privacy and the public sphere, which we call « society ».