“Don’t trust anyone over thirty.” This iconic 1960s phrase was coined by Jack Weinberg, a leader of the Free Speech Movement at the University of California, Berkeley. In Weinberg’s telling, he almost thoughtlessly tossed the line off during an interview with a reporter whose questioning implied that student activists were just a bunch of Communist dupes. “I told him we had a saying in the movement that we don’t trust anybody over thirty,” Weinberg recalled. “It was a way of telling the guy to back off, that nobody was pulling our strings.” But the phrase took on a life of its own and became something of a slogan for “the ’60s” as a whole —  youthful rebellion against a stultifying mass consumer society built by colorless middle-aged men in gray flannel suits. Against Weinberg’s intentions, it became an enduring call to arms in the battle between generations.

As a civil rights, free speech, and antiwar activist, Weinberg was a paradigmatic example of a New Left militant. What made the New Left new was its ostensible break with the Old Left of the 1930s and ’40s. There were good reasons for making this distinction. The Old Left was grounded in working-class, often immigrant, social milieus that found organizational expression in the Socialist and Communist parties as well as the trade unions. Nascent New Leftists were brought up after World War II, in a rapidly changing society defined by the growth of higher education, the burgeoning shift from industrial to service work, and the dissolution of ethnic proletarian communities. As a result, the New Left evinced a strong concern with movements and demands that hadn’t yet emerged in the New Deal period, and it had a fundamental commitment to “participatory democracy” that the Old Left did not share.

It’s not surprising, then, that New Leftists had a powerful sense of generational identity. The Port Huron Statement’s introduction is titled “Agenda for a Generation.” Its memorable first line, penned by a twenty-two-year-old Tom Hayden, is “We are people of this generation, bred in at least modest comfort, housed now in universities, looking uncomfortably to the world we inherit.” An Old Left manifesto would not have begun with an admission that it did not necessarily speak for an oppressed proletariat.