The study of cognitive development has been, and still is, faced with two fundamental problems. They are connected, and no satisfactory answer has been found to either. The first problem concerns a terminological distinction and the corresponding semantic contents - it is important to be clear about which characteristics make it possible to distinguish percepts from concepts proper. The second problem, which depends on such distinction, consists in determining when and how, in cognitive development, the turn from perceptual categories into (...) concepts occurs. This paper provides a clear and precise answer to both questions. (shrink)