Berlin addresses the issue of pluralism as the very idea of politics : it is because human beings do not share the same conception of life, of what is right and what is wrong that authority is necessary or life in a community compromised. It is worthy of note that pluralism is linked with the problem of (as Berlin puts it) « disagreement ». What is the nature of disagreement : it is a « disagreement about ends ». This entails an intellectual part, and, as such, is an intellectual phenomenon (though it is not solely an intellectual phenomenon). This explains what Berlin describes as « the power of ideas » and gives its chance to political thought. « Professors and thinkers » (think about the difference between the two) have a role to play in politics, which is not directly political, but which is nonetheless necessary and crucial.

 Pluralism is the very idea of liberalism. So liberalism is not only a political ideology (the ideology of liberty) among many others but drives us to the roots and the very essence of politics.
 This involves the relation between ideas and social forces (this is a critique of Marxists). Ideas might well be « stillborn » without the echo of social forces (p. 120), but these are without direction if no ideas do give them a sense. The meaning of society is not in society itself, but in a reflexive process about society.
 Without ideas, politics is reduced (for it is a reduction) to a technique. That is the St Simonian dream, but also the socialist and communist dream. We do not have to bother with ideas, but we have to use efficient tools to solve problems.
 That is why political philosophy is « a branch of moral philosophy ». It does not mean that politics should be the application of a moral perspective (that would eventually be illiberal for it would not allow the possibility of a diversity in values) ; far from it : it means that politics in itself produces values upon which we have to reflect.
 However, since pluralism is the essence of politics, « political thought » has « blurred edges » : no paradigm is fully satisfying, since we are in a plural context. Any truth has its limits. That is very important to understand many moves in Berlin’s text, which operates by assertions taken to their limits, and by clarifying those limits.

That, also, explains the way Berlin deals with the issue of liberty : first there are two concepts of freedom (so the definition of liberty is plural) ; but there is not even a clear-cut definition of it, because the attempt to get a definition ends up with more than 200 meanings for the word : what we actually have is two questions about liberty. It happens that sometimes questions are clearer than definition.