Online discourse has created a new media environment for contributions to public life, one that challenges the social significance of the role of public intellectuals?intellectuals who, whether by choice or by circumstance, offer commentary on issues of the day. The value of such commentary is rooted in the assumption that, by virtue of their training and experience, intellectuals possess knowledge?that they understand what constitutes knowledge with respect to a particular topic, are able to distinguish it from mere opinion, and are in a position to define its relevance in different...