Gullibility, carelessness and closed-mindedness are examples of what the US philosopher Linda Zagzebski, in her book Virtues of the Mind(1996), has called ‘intellectual vices’. Others include negligence, idleness, rigidity, obtuseness, prejudice, lack of thoroughness, and insensitivity to detail. Intellectual character traits are habits or styles of thinking. To describe Oliver [who believes 9/11 was an inside job] as gullible or careless is to say something about his intellectual style or mind-set – for example, about how he goes about trying to find out things about events such as 9/11. Intellectual character traits that aid effective and responsible enquiry are intellectual virtues, whereas intellectual vices are intellectual character traits that impede effective and responsible inquiry. Humility, caution and carefulness are among the intellectual virtues Oliver plainly lacks, and that is why his attempts to get to the bottom of 9/11 are so flawed.