In his dramatic works, Shakespeare sometimes resorted to the philosophical ideas of late Antiquity, first proclaimed by "the last Roman" Boethius in his treatise De Institutione Musica. Inspired by the Pythagorean-Platonic tradition, Boethius divided music into the objective music of the cosmos (musica mundana) and the subjective music of the human soul (musica humana). His philosophy is connected with the idea of the musical nature of Being. According to Boethius, the cosmos is structured on the principle of musical proportionality. The relations between heavenly spheres are equal to those between musical intervals. Seven heavenly spheres form a heavenly heptachord, whose every planet corresponds to a certain string of a kithara, i.e., the cosmos is imagined as a huge musical instrument (Boethius 1867: 188-189). And if the human ear can no longer hear the sounds of heavenly music, the reason is our force of habit: we become so accustomed to its sounds, that we stop distinguishing them. In European Christian culture, this idea was transformed as follows: heavenly music can't be heard by people because of their imperfection, as that kind of music is of divine and eternal nature, like the singing of angels.
The second kind of music according to Boethius is human music (musica humana). Everybody who pays attention to his/her inner self can understand it. This music is a reflection of the indivisible human essence and is the expression of man's inner world. Both world and human music are united by the principle of harmony, which is capable to turn essentially different phenomena into a single one. So music puts in order not only the cosmos, but also the human being, harmonically uniting flesh and soul. Thus the two kinds of music that Boethius speaks of are like two directions of a human being's way of looking: upwards--to the stars, and within--into one's heart.
Boethius music theory also includes a third kind of music, instrumental or sound music (musica instrumentalis), i.e., music in the true sense of the word (Boethius1867:191). Instrumental music may have such a great influence on the human being that it can be used for healing or in education. In connection to this, let us remember an ironic cue by Shakespeare's Benedick in Much Ado About Nothing: "Now, Divine air! Now is his soul ravisht!--Is it not strange that sheeps' guts should hale souls out of men's bodies?" (II.3.54-56).
Boethius' music theory was taken over and developed by Renaissance aesthetics and was reflected in the works of art by Renaissance authors. From this point of view, Shakespeare's dramatic works are of special interest, because music is present in them in many universal ways.
For Shakespeare, music was the harmony of heavenly spheres, just like for his older contemporary, Philip Sidney, who spoke of the "planet-like music of poetry" (Sidney 1973:121). In a famous musical episode in The Merchant of Venice, Lorenzo compares the movement of heavenly bodies that "like an angel sing" with the harmony of "immortal souls":
Look, how the floor of heaven
Is thick inlaid with patines of bright gold;
There's not the smallest orb which thou behold'st
But in his notion like an angel sings,
Still quiring to the young-ey'd cherubins;
Such harmony is in immortal souls;
But whilst this muddy vesture of decay
Doth grossly close in it, we cannot hear it
In Shakespeare's plays one can also hear music in the human soul. Anticipating the poetics of Romanticism, Shakespeare sees music as the true language of the senses. But at the same time, he combines musical and moral values, presenting virtue as inner music, which is close to the tradition of medieval Christian ethics. The close interweaving of musical and moral terminology characterizes many of Shakespeare's dramatic works. Here is again an example taken from The Merchant of Venice:
The man that hath no music in himself,
Nor is not mov'd with concord of sweet sounds,
Is fit for treasons, stratagems, and spoils;
The motions of his spirit are dull as night,
And his affections dark as Erebus:
Let no such man be trusted. …