What’s at stake in the struggle between Nancy Pelosi and the four progressive House members known as the squad? Partly it’s just the perpetual conflict between younger members who want change fast and older members who say you have to deal with political reality.

But deep down it’s a conflict of worldviews. No matter how moderate or left, Democrats of a certain age were raised in an atmosphere of liberalism. I don’t mean the political liberalism of George McGovern. I mean the philosophic liberalism of people like Montaigne, John Stuart Mill, Abraham Lincoln and Frederick Douglass — people who witnessed religious and civil wars and built structures to restrain fanaticism.

Philosophic liberalism, Adam Gopnik explains in his essential book, “A Thousand Small Sanities,” begins with intellectual humility. There’s more we don’t know than we do know, so public life is a constant conversation that has no end. In the liberal view, each person contains opposites and contradictions. You flatten and dehumanize complex individuals when you see people according to crude dichotomies and assign them to tribal teams.

Liberals prefer constant incremental reform to sudden revolution. “Liberal reform, like evolutionary change, being incremental, is open to the evidence of experience,” Gopnik writes. Liberals place great emphasis on context. The question is not: What do I want? It’s: What good can I do in this specific circumstance?