I examine Zhu Xi's investigation thesis, the claim that a necessary condition (in ordinary cases) for one’s acting fully virtuously is one’s investigating the all-pervasive pattern in things (gewu格物). I identify four key objections that the thesis faces, which I label the rationalism, elitism, demandingness, and irrelevance worries. Zhu Xi, I argue, has resources for responding to each of these worries, and for defending a broadly intellectualist conception of fully virtuous agency.