Of great interest to cognitive science is how human learning is constrained to avoid spurious generalizations. While many constraints must be relatively experience-independent, past experience provides a rich source of guidance for subsequent learning. If a learner discovers some structure in part of the environment, this can inform her future hypotheses about that domain. If a general structure parsimoniously accounts for particular sub-patterns, a rational learner should not stipulate separate explanations for each detail without additional evidence, as the general structure has “explained away” the original evidence. In a grammar-learning experiment using tone sequences, manipulating learners’ prior exposure to a tone environment affects their sensitivity to the grammar-defining feature, in this case consecutive repeated tones. Grammar-learning performance is worse if context melodies are “smooth”, that is, if small intervals occur more often than large ones, as this smoothness is a general property that accounts for a high rate of repetition.