Four experiments explored an asymmetry in the perceived similarity of melodies: If a first-presented melody is "scalar" (conforms to a diatonic major scale), and is followed by a second melody slightly altered to be " nonscalar" (deviating from a diatonic major scale), subjects judge similarity to be lower than if the nonscalar melody comes first. Experiment 1 produced evidence that asymmetric similarity is not due simply to more strongly scalar melodies having greater memorability. Experiment 2 ruled out the hypothesis that asymmetric similarity depends on a taskspecific strategy reflecting demand characteristics. Experiments 3 and 4 replicated asymmetric similarity while controlling the number of onesemitone intervals in scalar versus nonscalar melodies. The data are consistent with Garner's principles that stimuli are perceived with reference to sets of alternatives and that good stimuli have few alternatives. Specifically, when melodies are presented in scalar—nonscalar order, but not when presented in nonscalar-scalar order, the first melody evokes a small set of alternatives which the second melody often violates.