The single affect principle is a musicological term describing the idea that contrasting affects (moods or sentiments) cannot belong in the one and the same musical movement,[1] the harmonic structure of which would thus be limited by enharmonic modulations. It was one of the defining characteristics of pre-Classical period music (Renaissance music, Baroque music, etc.), and gradually became obsolete ca. 1800. There has been a resurgence of its use in contemporary historicist and minimalistmusic.