Following from an earlier analysis by B. F. Skinner, the present article suggests that the verbal processes in science may usefully be viewed as following a three-stage progression. This progression starts with (a) identification of basic data, then moves to (b) description of relations among those data, and ultimately concludes with (c) the deployment of higher order concepts in statements about organizations of data. The article emphasizes the importance of viewing theory and explanation as examples of verbal processes at the later stages, guided by the stimulus control from the earlier stages. The article further suggests that many theories and explanations in traditional psychology often take a form that appears to be from the later stages. However, adequate activity at the earlier stages has not preceded those theories and explanations. They therefore do not have the benefit of suitable stimulus control from the earlier stages. Rather, they reflect some degree of stimulus control by many mentalistic assumptions about causal entities and relations. Ultimately, traditional theories and explanations influenced by mentalistic assumptions occasion less effective interaction with natural events (e.g., through prediction and control) than they might otherwise.