Song and Soul
It is a truism that song touches the soul. Something about song and something about the soul naturally mesh: that is, song and the emotions are suited to one another. But why is this? What features suit song to the emotions and hence the soul? Song is clearly language set to music, but what is language and what is music? Language is the pairing of sound and meaning, or better the union of the two: sound expresses meaning and meaning suffuses sound. Music is the union of melody and rhythm: pitch variations conjoined with temporal intervals. So song is the union of these two unions: a song is the joining together of the sound-meaning pair (language) and the melody-rhythm pair (music). When you sing you are fusing your ability to conjoin sound and meaning with your ability to conjoin pitch variations and temporal intervals. A song is a synthesis of these four elements: sound, meaning, melody, and rhythm. In a song, language is converted into something temporally structured (bars, note lengths) and pitch variations are imposed on it (the standard musical scales). Language becomes music. So there is a metamorphosis into an aesthetic medium, no longer a mere vehicle of communicative speech. Language is called upon to operate in the realm of art. Meaning itself becomes an aesthetic object by being subjected to musical forms. The speech act of song is a distinctively aesthetic type of speech act. And music itself becomes imbued with the representational power of language: it acquires an extra layer of meaning, a new type of significance. Music becomes semantically complex, doubly expressive. Such are the powers of song to transform both language and music into new versions of themselves.
But how do these constitutive features of song mirror the emotions? One would like to find parallel structures at work in the emotions. First, sound and meaning: what in the emotions parallels this duality? Surely this: emotions admit a distinction between their felt character and their representational content. It feels a certain way to be angry or in love and these emotions are about certain people and states of affairs—what philosophers call qualia and intentionality. Moreover, these features merge and meld: they are not independent dimensions like size and color. So emotions are structurally similar to language in joining the phenomenological and the referential—a coloration of consciousness and a semantic content. Second, melody and rhythm: how do emotions parallel thisdistinction? Certainly not by sounding like higher and lower notes, or by mimicking the sound of a drum; but at a more abstract level we can find similarities. Pitch intervals consist of variations along a continuum of sound, selections from acoustic space; and rhythm is the spacing of sounds over time. But don’t emotions also vary continuously in an analogous way, and don’t they also occur spread out in time as separate experiences? Your anger can reach a high affective pitch, waxing and waning, then give way to something less intense; and it can also develop over time according to a recognizable pattern. Your love can burn brightly or dim languidly, and it also throbs and pulses in predictable ways (as when you meet or part from the beloved). Emotions evolve in time and they can be more or less intense (sharp, deep, tormenting, exhilarating). They can also be repetitive and maddening (or soothing). They can reach a crescendo or peter out, scale new heights or plumb new depths. Emotions seem to possess a “music” of their own: staccato or smooth, vibrant or torpid. So emotions mirror the musical form of a song, as well as its linguistic form. As the song progresses, its melody and rhythm intersect with the phenomenology of the corresponding emotions, in such a way that a certain note seems to condense a whole world of emotion, capturing the emotion perfectly. The music of the song maps onto the “music” of the emotions, with its variations of pitch and temporal development. Thus a song can condense and encapsulate a familiar human emotional experience, say the breakup of a love affair. There is an underlying commonality of form. The fourfold union of song reflects the fourfold union of emotion: sound-meaning plus melody-rhythm mirrors feeling-meaning plus affective variation combined with temporal development. The song is targeting the emotional structures of the soul. 
And there is a further similarity, namely the close connection between the inner and the outer that characterizes both song and emotion. Emotion characteristically has a behavioral expression, both vocal and non-vocal, as when a person shouts and stamps his feet; but song too, like most music, is often accompanied by behavioral expression, as in swaying and dancing. Musical experience and emotion both tend to translate into bodily movement. So hearing a song is apt to lead to the same kinds of behavior that the corresponding emotions lead to—swooning, jumping up and down, lachrymation. The emotions have their bodily manifestations, and so does hearing a song. This affinity enables song to connect with emotion, just as if a song were an embodied emotion. Also, the connection between the inner and the outer in the two cases is not an external connection: the behavior is integral to the emotion (in a way notoriously hard to articulate). The inner and the outer are unified. So there is a third union to be added to the previous two: both song and emotion are the union of three unions. Song is thus the ideal vehicle for the expression of emotion: they both have the same abstract architecture. The soul sings. 
 Similar remarks may be made about poetry and emotion: the affinity is undeniable, and it is natural to find in emotion some of the structure of poetry—meter, assonance, dissonance, etc. Song, of course, is a form of poetry, as well as being a form of music. A song is poetry set to music, and this enables it to tap into the emotions via the formal analogies between the two.
 Less poetically, the emotions are analyzable using much the same conceptual apparatus that we can use to analyze the nature of song. The two are isomorphic, formal twins. That is why a song feels like an aural emotion.