In National Review's 50th anniversary issue, Charles Murray reviews Thomas Sowell's 1987 book, A Conflict of Visions (link to Murray's article requires subscription):

One mark of a great book is a thesis so powerful that after a few years people take it for granted. Thomas Sowell’s A Conflict of Visions (1987) is such a book. Its thesis: The policy arguments between liberals and conservatives, socialists and libertarians, do not arise just from differences in priorities regarding freedom, equality, and security. At root, they draw from different conceptions of the nature of man. The Left holds an unconstrained vision: Given the right political and economic arrangements, human beings can be improved, even perfected. Success is defined by what people have the potential of becoming, not by people as they are. The Right holds a constrained vision: People come to society with innate characteristics that cannot be reshaped and must instead be accommodated. Success in political and economic policy must be defined in light of those innate characteristics.

Once you have this framework in your head, the history of the great political debates of the 20th century coheres in a new way. The expansion of the welfare state, how to deal with crime, how to conduct the Cold War, the feminist revolution, colorblind policies versus affirmative action, who should control the schools — whatever the topic, the positions held by Left and Right make sense in terms of each side’s underlying vision of the nature of man.

A second mark of a great book is that it clarifies events that occur after its publication. Sowell wrote A Conflict of Visions during the 1980s, when the modern-liberal vision still had life and the influence of the classical-liberal vision was at its height. People on both sides still knew why they were so passionate about their political beliefs. Now we have the passion, but no why. The political climate is more partisan and bitter than ever, but what are we fighting over? Sowell’s thesis is useful in understanding this new environment.

Start with the Left. The difference between the Left of the 1960s and that of 2005 is that the politicians of the Left no longer believe in human malleability. The last two decades have refuted every basis for that belief, from the failure of Communism to the accumulating science of innate human nature. And so we end up with a politics of the Left stripped of the idealism that used to dignify even its most wrongheaded positions. The Left used to say that people were driven to crime by poverty and that the real crime was to punish them. Now the Left complains about too many people in prison, but it’s a cost/efficiency issue. The Left used to say that greater equality of income would lead to a happier society for everyone. Now the Left tries to play the envy card, but without the egalitarian idealism. On issue after issue, mainstream politicians of the Left no longer even try to appeal to the prospect of changing human beings for the better. Liberalism has become reactionary, trying to hold on to terrain it occupied in the Thirties and Sixties. Using Sowell’s language, we are watching what happens when Democrats have lost faith in the unconstrained vision of the nature of man and have not found anything to replace it.

More Murray:

Now apply Sowell’s explanatory template to the Right. From the founding of National Review — an opening date that I nominate without fear or favor — through the presidency of Ronald Reagan, the intellectual vigor of the constrained vision grew. Then, during the 1990s, we discovered how much the vigor of the constrained vision depended on competition. With the Left intellectually moribund, politicians of the Right began to take the easy way out. It is understandable, because advocating the policies of limited government is psychologically uncomfortable. It requires a politician to say he wants to do things that will cause pain — cut benefits for young women with babies, scrub regulations that putatively protect the environment, or end affirmative action. A decent person can endorse such actions only if he believes that they are essential for the ultimate good, and that means being steeped in the wisdom of the constrained vision of the nature of man. In the aftermath of the Reagan ascendancy, when running and winning as a Republican became so much easier, we got more and more Republicans who wanted to be nice guys. George W. Bush is their leader. And so we have watched a Republican-controlled government take a giant step toward federalizing public education through the No Child Left Behind Act; add a major new unfunded entitlement to Medicare; and, last summer, demonstrate that Republicans in power love pork as much as the Democrats ever did. We are watching what happens when Republicans have forgotten the constrained vision of the nature of man and replaced it with a fuzzy desire to do good.

Update: Speaking of Sowell, he has a brief list of recommended books for Christmas presents at TownHall.com.