Some dimensions such as size and loudness are clearly marked for magnitude with one end being "more than" the other end. Thus, big is more than little and loud is more than quiet. This research examined the interaction of perception and language in the development of the magnitude marking of size, loudness, and achromatic color. Children 2 to 5 years of age and adults participated in six experiments. A cross-dimension matching task and a "Which is more?" task were used. The results suggest fast, invariant, and unidirectional development for size and loudness. Big is perceptually and linguistically more than little early in development and becomes more strongly organized with development. Loudness starts out disorganized and may be linguistically organized into more and less ends before it is perceptually organized. However, developments in perception and in language are rapid and in the same direction. In contrast, achromatic color shows an irregular developmental trend. Early in development, dark grey is perceptually more than light grey. But this early organization is disrupted at the same time that children acquire the words dark and light. The results suggest converging interactions between perception and language in the case of size and loudness and antagonistic interactions in the case of darkness. The results are interpreted in terms of a dynamical system.