Here is a column by Michael Barone. I now think that both progressivism and conservatism stem from liberalism, which is a contested concept. (Think of liberalism as a tree trunk and the others as its two main branches.) Liberals such as John Stuart Mill (1806-1873) defend freedom of expression. Conservatives want to conserve this liberal tradition, while progressives want to constrain speech that they believe has harmful, offensive, or inegalitarian effects. The opposition between liberalism and conservatism is misleading, at least if liberalism is understood as classic (Millian) liberalism. Conservatives are classic liberals. Progressives are egalitarian liberals. Conservatism can be viewed as resistance to the hijacking of liberalism by egalitarians.