The blossoming of "humanism" in the Renaissance meant that humans were seen less as creatures and more as creators. The fierce authority of the cantus firmus was ousted and, instead of the rhythmically driven polyphony of the late Middle Ages, 15th- and 16th-century music in Europe valued melodic beauty, expressiveness, and unity. Composers of even cyclic Masses valued aesthetics above liturgical concerns (Brown 3). Unlike the case with most of the other arts, Renaissance composers could not immerse themselves in Classical tradition: little Greek music survived and probably was not decipherable until a later century. So Renaissance composers were free to explore new innovations.
The English are atypically on the cutting edge in the arts, but were for a rare period in the 1400s in music (and then again at the end of the 1500s). Using "faburden, a technique of inserting an improvised 'harmonic' part between two written parts," the English carols sounded very new harmonically because the third now often sounding with the tonic and and fifth in chords: "The result was a kind of enriched, vertical and highly euphonious harmonic descant" (Fritz 101). In other words, triads were now considered sonorous. Partly because of the English victory at Agincourt in 1415, this style spread on the continent. Eventually a French-Flemish musical renaissance emerged, and so indeed did nationalism, so that individual countries formed their own musical dialects. In general, though, the V-I (dominant to tonic) cadence predominated and crystalized the starts of a system of functional tonality.
The chief forms of music in these centuries were Masses, settings of secular lyric poetry (such as French chansons, Italian madrigals), and motets (but not the outrageously complex types from earlier). "The emancipation from medieval ways of thought and the restrictions of pre-formed structure meant that music became for the first time a self-sufficient, self-generated art" (Brown 3). Thus, instrumental music, "an 'absolute art' not related to literary meanings and preconceived patterns" (Brown 3), started receiving important attention too, so much so that lyrics tend to recede into the background and not until Monteverdi do they emerge forth again in balance with the music (Fritz 101).
Expressivism, the idea that the music should reflect the text, became more important in the sixteenth century. Monteverdi's "Zephiro torna" is a good example, almost mannerist, in fact.
Zefiro torna e di soavi accenti
L'aer fa grato e'l pie discoglie a l'onde
E mormorando tra le verdi fronde
Fa danzar al bel suon sul prato i fiori,
Inghirlandato il crin Fillide e Clori,
Notte temprando amor care e gioconde,
E da monti e da valli ime e profonde
Raddopian l'armonia gli antri canori.
Sorge più vaga in ciel l'aurora, e'l sole
Sparge più luci d'or, più puro argento
Fregia di Teti il bel ceruleo manto.
So io per selve abbandonate e sole
L'ardor di due begli occhi e'l mio tormento
Come vuol mia ventura hor piango, hor canto.
Return O Zephyr, and with gentle motion
Make pleasant the air and scatter the grasses in waves
And murmuring among the green branches
Make the flowers in the field dance to your sweet sound;
Crown with a garland the heads of Phylla and Chloris
With notes tempered by love and joy,
From mountains and valleys high and deep
And sonorous caves that echo in harmony.
The dawn rises eagerly into the heavens and the sun
Scatters rays of gold, and of the purest silver,
Like embroidery on the cerulean mantle of Thetis.
But I, in abandoned forests, am alone.
The ardour of two beautiful eyes is my torment;
As my Fate wills it, now I weep, now I sing.
From the Renaissance come keys, cadences, tonic insistence, regularity of stanzas, and pinning music to text -- all in ways incalculably more familiar to us than the principles of medieval music. Is this rule-driven aesthetic in the art(s) all because medieval "stability" is gone?
Consider medieval "Christendom" in light of the "threat," especially intense from the 1950s through the 1980s, of the Soviets taking over the world.
There was a relative looseness of regional inflections when Christendom ruled, vs. divisive and rigid parochial subdivisions and defensiveness during the Protestant Reformation.
The Reformation was suspicious of artistic beauty. When it came to music, the new order insisted on regularity and simplicity in inane blockline chunks (hymns). Calvinist distrust of music yielded puritan American impulses we inherit today.
So less social stability and security = increased repetition and impulsive insistence on stability in the arts? less freedom, more neurosis?
Brown, Howard M. Music in the Renaissance. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1976.
Fritz, Heidi. "Dawn of the Renaissance." Trans. Derek Yeld. Les Tres Riches Heures du Moyen Age: A Medieval Journey. Arles: Harmonia Mundi, 1995.