Wallace (1966) proposed that personality be construed as a set of abilities. Rather than assessing typical performance, as in trait ratings, he recommended assessing an individual's ability to perform social behaviors. We have elaborated this notion by distinguishing between personality abilities and capabilities. In this article we focus on the capability, that is, the ease with which an individual can display a certain category of social responses. A capability X is assessed with self-reports of (a) likelihood of performing X when perceived to be required, (b) perceived difficulty in performing X, (c) anxiety in performing X, and (d) tendency to avoid performing X. In Study 1 we examined the relations among six measures of 16 interpersonal behaviors in the context of the interpersonal circumplex. The four capability-related measures were shown to be measuring something distinct from the two trait measures. Unlike trait measures, which showed a circular structure in two dimensions, capability measures exhibited a positive manifold structure (i.e., no negative intercorrelations). The first two orthogonal factors were interpreted as Hostility and Nurturance, which are normally bipolar opposites on trait measures. Thus individuals capable of hostility are also capable of nurturance. The only dimension to remain bipolar was introversion-extraversion. In Study 2, the nomological network of the capability measures was shown to be consistent with the theoretical construct. For example, high self-esteem and interpersonal control were associated with almost all of the interpersonal capabilities. Almost 20 years ago, Wallace (1966, 1967) elaborated the view that personality attributes are better construed as abilities than as traits. He noted that an individual's tendency to display a behavior is a function of the ability to perform the behavior moderated by situational variables like inhibition and lack of incentive. Thus individuals may not typically be dominant either because they are not able to be dominant (i.e., they lack the necessary skills) or because their dominant predisposition is typically inhibited. By failing to address this distinction, standard trait conceptions of typical or average behavior confound ability deficits with response inhibition. To assess a person's response ability, Wallace argued that the assessor must provide the optimal situation for that person to display it. Once such an ability is confirmed (or disconfirmed), the assessor is in a better position to make a decision regarding job placement, social skills training, or psychotherapy, as the case may be.