Music is often associated with the emotions of nostalgia and longing. According to previous survey studies, both nostalgia and longing are among the most common emotions evoked by music (Juslin, 2011). Despite nostalgia's significance as a musical emotion, research on the specific properties of music that might contribute to this particular emotion has been scarce. A recent empirical experiment by Lahdelma and Eerola (2014) sought to explore whether single chords could be effective at conveying musical emotions to listeners, which spanned complex emotions such as nostalgia/longing. According to the results, single chords such as the minor triad, the minor seventh and especially the major seventh communicated the emotion of nostalgia effectively. The aim of the current paper is to raise several possible explanations that might account for the ability of single chords to convey the emotion of nostalgia. In these explanations we consider cultural, music-theoretical and psychoacoustic issues, as well as their possible interactions. The three proposed candidate explanations are (1) learning, (2) intrinsic emotional connotations arising from tonal relations, and (3) clashing conventions arising from concurrent yet separate affective associations, stemming from certain triad and interval combinations. Finally, we propose experimental designs for future research to empirically test these explanations.Submitted 2014 November 17; accepted 2015 September 8. KEYWORDS: chord, vertical harmony, emotion, nostalgia, longing NOSTALGIA is a common emotion (Boym, 2001), described as a universal experience that transcends age groups and is present across the lifespan (Sedikides, Wildschut, & Baden, 2004). According to Wildschut, Sedikides, and Routledge (2008), the term nostalgia "derives from the Greek words nostos (return) and algos (pain)" (p. 20), literally meaning "the suffering evoked by the desire to return to one's place of origin " (p. 20). The New Oxford Dictionary of English (1998) defines nostalgia as "a sentimental longing or wistful affection for the past" (p. 1266), underlining the longing quality inherent in the emotion. According to Batcho (2007), "most theorists agree that the distinctive emotional character of nostalgia is bittersweet -a mix of sadness and wistful joy" (p. 362). Sedikides, Wildschut, Arndt, and Routledge (2008) propose that "nostalgia is triggered by dysphoric states such as negative mood and loneliness" (p. 304), but that it also generates positive affect. Nostalgia's positive effects have also been reported by, for example, Juhl and Routledge (2013) and Cheung et al. (2013).These positive effects could be one reason why music is often called for to induce nostalgia, as music is a common source of nostalgia (e.g., Barrett et al., 2010;Zentner, Grandjean, & Scherer, 2008), and it often serves a nostalgic function in everyday life (Juslin, Harmat, & Eerola, 2013). Juslin (2011) proposes that on the basis of previous survey studies both nostalgia and longing are among the most common e...