I was teaching the day the airplanes hit the World Trade Center. It was the second meeting of “The Communist Manifesto for Seminarians,” a course for my fellow graduate students. By the time I got to class, both towers had collapsed. A few hours later, Building 7 came down as well. We dispensed with a planned discussion about what Marxists mean by “idealism” and “materialism” and talked instead about the meaning of this particular example of the “propaganda of the deed.”