We propose the interrogative investment hypothesis: the basic interrogative forms can serve as units for describing how individuals come to differ in cognitive competence. These forms fall into two levels. Questions of object (what, where, who, when, how many) carve reality into aspects; questions of reason (how, why) relate these aspects and underlie methods of inquiry such as the historical and scientific methods. Gardner's theory of multiple intelligences offers a rich description of these differences; we propose a complementary developmental mechanism that may help explain how its profiles take shape. In line with Hayes's (1962) motivational-experiential theory of intelligence, we suggest that its domains are strengthened, at least in part, through investment. A spontaneous preference for one kind of question draws attention and time toward it; because time is scarce, this produces cumulative practice, growing competence and increasing reward, which strengthens the preference in turn. We discuss where such preferences may come from: inherited dispositions, early ability, the answers children receive, and culture. Hayes's experience-producing drives were never operationalised; we suggest that question preferences could provide one possible behavioural indicator of them. We propose a simple task to capture these preferences, a pilot study with explicit criteria for failure, and five testable predictions. Finally, we draw implications for education: questions show where a child's attention goes before competence is visible, one object can be taught through many questions, and the way adults answer may shape which questions grow. The proposal is theoretical; no data have been collected.
Version 5. Adds a section on the origins of question preferences with a fifth prediction, a pilot study with criteria for failure, and a section on implications for education.