The traditional approach to the analysis of knowledge sees it as a true belief meeting further conditions. I discuss an empirical challenge to this traditional approach, which I call the argument from development. Briefly, the argument is that belief cannot be conceptually prior to knowledge because children acquire the concept of knowledge first. Several prominent scientists and philosophers have argued that this latter claim is supported by many findings with infants and young children. Here, I defend the traditional approach by (...) raising three challenges to the argument from development: the competence-performance challenge, the double-standard challenge, and the underdetermination challenge. I conclude that the developmental data are fully compatible with children acquiring the concept of belief first. In closing, I also argue that further research is needed to investigate when children acquire a concept of knowledge. (shrink)