Five perceptual principles of melodic implication, derived from Narmour's (1990, 1992) ``implication-realization'' theory of melody, were evaluated in an analysis of European folk songs. The principles apply only to unstable or unclosed melodic conditions, and define how such conditions initiate processes of pattern recognition which then generate expectations about the properties of subsequent notes. For instance, the principle of proximity states that unstable events generate an expectation that the next note will be proximal in pitch. Musically stable and unstable events were identified in over 700 melodies, using criteria based on metric stress, tonality, and duration. For each event, the next note (the continuation note) was recorded. Multinomial loglinear analysis assessed whether the five principles, separately or in combination, could predict the frequency with which different continuation notes followed different conditions of stability. For continuation notes following unstable events, statistical support was found for all principles. The link between musical stability, melodic expectation, and composition is discussed.