How do new ideas spread through a population? Some persons, whom we may call "thought leaders," naturally grasp a new idea at an earlier stage, while other "thought followers" come to understand it only after it has been widely circulated and articulated and developed by the thought leaders. Such differences among people arise in part because some individuals are afraid to think independently, and in part because of natural differences in intellectual exposure and ability. The thought leaders therefore offer a kind of leverage point for intellectual change in a society. For maximum effect, therefore, the effort of intellectual activism should be directed toward this stratum.