Trait breadth and hierarchical organization are central structural principles in personality theory and research. We assume that personality traits serve as categories of behavioral events, and we define the breadth of traits as the diversity of their behavioral manifestations. We show that trait breadth can be measured reliably both by ratings and by direct comparisons within trait pairs. We assess the hierarchical relations between traits differing in breadth, using a task in which subjects select the most meaningful of two statements, such as "To be talkative is a way of being extroverted" versus "To be extroverted is a way of being talkative." The extent of asymmetry in the choices of the subject sample provides an index of the degree of class inclusion. In four studies, we demonstrate that the size of the asymmetry effect is highly predictable from differences in trait breadth, even when the effects of social desirability, familiarity, and meaningfulness are controlled. Moreover, we replicate these findings in two cultural contexts, and even at the level of individual subjects. The availability of traits at different hierarchical levels requires personality psychologists to make an explicit choice about level of abstraction, especially when studying behavioral consistency. We discuss the prospect for identifying a generally preferred or "basic" level of personality description.