The problem with "conservative" is that it's such a slippery term. Unlike liberalism, nationalism, or socialism, conservatism isn't a distinct ideology. Instead it feeds off other ideologies, which is why we can speak of "conservative capitalists" or "conservative socialists." What compounds the problem of a definition is that the "host ideology" can change from one location and time period to another.

But while conservatism does not present a universal pattern for all times and all places, there are certain similarities that are generally consistent. Russel Kirk outlines six common principles that help us to define the essence of conservatism:

1. The principle of moral order -- a belief in a transcendent moral order to which we ought to try to conform the ways of society.
2. The principle of social continuity -- Conservatives prefer the devil they know to the devil they don't know.
3. The principle of prescription -- A reliance on the "wisdom of our ancestors."
4. The principle of prudence -- Public measures should be judged by their long-term consequences.
5. The principle of variety -- A healthy inequality is necessary for civilization.
6. The principle of imperfectability -- Since man is imperfect, no perfect social order can be created.

Obviously, this framework can be built on very different foundations. While the principle of moral order may agree that there is a "natural law" it could be developed from different traditions, such as Thomism or Stoicism. As in chaos theory, a small difference could lead to drastically different outcomes. While both may be classified as "conservative," their conclusion could vary significantly. That is why it is often misleading to compare and contrast different strains of conservatism as if they were descended from the same ideological bloodline.

As a political philosophy conservatism is certainly not without its flaws. History shows that it has been used to protect power and privilege for the "haves" against the "have nots" or to rationalize injustices that are fitting within a particular "tradition." But the core of conservatism, it's "politics of prudence", makes it the best possible guide for out future. What Winston Churchill said of Democracy could apply equally well here: Conservatism is the is the worst political theory…until you consider the alternatives.

Update: Matthew Stinson takes up this them also and shows that the same conclusion could apply to American liberalism.