Section 4.3 then examined Isaiah Berlin's analysis of the difference underlying positive and negative liberty. Positive liberty, Berlin argues, is grounded on monism--the belief that all values ultimately are harmonious and that a single answer can be uncovered to the question, "What makes life worth living?" In contrast, Berlin believes that negative liberty is supported by pluralism, a conviction that the ends in life are many and conflicting. Because there are many good things in life and we cannot have them all, we must choose, but it does not seem that any one choice is demanded by reason. Hence the importance of negative liberty. I extended Berlin's point, showing how positive liberty reflects rationalism and allegiance to a self-developmental view of human nature. This combination of rationalism and self-development views of human nature characterized much of the "new liberalism" that arose at the beginning of the twentieth century, thus helping to explain why new liberal theorists tended to adopt positive conceptions of liberty. In contrast, the classical liberal tradition has been far less prone to accept either rationalism or self-developmental views of human nature, and has tended to stress moral individualism and pluralism.
In Section 4.4, I examined two challenges to the stark contrast between negative and positive liberty. Gerald MacCallum tries to show that all freedom claims--negative as well as positive--have a three-part structure; he insists there is but one concept of liberty. Last, I argued that we should be careful not to overstate the differences between negative and positive liberty, since even advocates of negative liberty must concern themselves with the internal conditions for genuine choice. Only choosers can be denied political liberty. Nevertheless, although the distinction is not quite so stark as some have thought, it seems that Berlin has made out a powerful case that the different interpretations of liberty are grounded on different, indeed competing, understandings of value, reason, and human nature.