(DCA) Yuval Levin offers this definition (h/t Robert Pondiscio):

To my mind, conservatism is gratitude. Conservatives tend to begin from gratitude for what is good and what works in our society and then strive to build on it, while liberals tend to begin from outrage at what is bad and broken and seek to uproot it.

You need both, because some of what is good about our world is irreplaceable and has to be guarded, while some of what is bad is unacceptable and has to be changed. 

This is a thoughtful effort to describe left and right evenhandedly, but I don’t think it is the best way to define or defend conservatism.

The problem is that people differ greatly in the degree to which they can reasonably be grateful to any particular polity. Consider, as one of several extreme examples, Native Americans. They can adopt any view of the USA that they want, but they have much less objective reason to be grateful to this republic than I have. They may well feel deep gratitude to their own communities. That gratitude is particularistic. Conservatism would then imply a particularistic ideal: a commitment to the specific communities that deserve each person’s gratitude. Some versions of conservatism have in fact been particularistic–but not Levin’s. He wants Americans (all Americans, I presume) to feel grateful to the nation-state:

But we can also never forget what moves us to gratitude, and so what we stand for and defend: the extraordinary cultural inheritance we have; the amazing country built for us by others and defended by our best and bravest; America’s unmatched potential for lifting the poor and the weak; the legacy of freedom—of ordered liberty—built up over centuries of hard work.

In the same essay, Levin suggests a more secure and persuasive core principle for conservatism—humility:

Conservatives often begin from gratitude because we start from modest expectations of human affairs—we know that people are imperfect, and fallen, and weak; that human knowledge and power are not all they’re cracked up to be; and we’re enormously impressed by the institutions that have managed to make something great of this imperfect raw material. So we want to build on them because we don’t imagine we could do better starting from scratch.

This reminder of “modest expectations” is what conservatism valuably contributes to public debates. Because people are “imperfect, and fallen, and weak”–or, we could say, cognitively and motivationally limited and biased–we should always be somewhat skeptical of ambitious reform proposals, of original designs for complex things (cities, welfare programs, markets), and of the likelihood that any person can dramatically improve things for any other person.

Humility, in this sense, is the common thread that unites libertarians (skeptical of central planning), religious conservatives (skeptical of human reason and motivation), and communitarians (skeptical of formal institutions). It also encourages all three types of conservatives to admire complex phenomena that have emerged and that seem to function well enough–“that have managed to make something great of this imperfect raw material.”

Levin argues that humility implies gratitude, but that connection is contingent. It depends on whether what has emerged so far is good enough for you and the people you care most about. Answers to that question will reasonably differ. Humility is the premise; gratitude is a consequent that depends on the circumstances. Humility is something that everyone has a reason to endorse, although everyone should also be open to the possibility of change.

See also: what defines conservatism?; a plea to conservatives; and from classical liberalism to a civic perspective