Contemporary Period

Why do musical styles change? The "evolution" of music is at least partly
shaped by the influence one composer has on another. These influences
are not always positive, however. Sometimes composers react against
the music of their recent past (even though they might admire it) and move
in what seems to be the opposite direction. For example, the simplified
style of the early Classical period was almost certainly a reaction to the
extreme intricacies of the late Baroque.
The late Romantic period featured its own extremes: sprawling
symphonies and tone-poems overflowing with music that seemed to
stretch harmony and melody to their limits. It is certainly possible to view
some early 20th century music as an extension of the late Romantic style,
but a great deal of it can also be interpreted as a reaction against that
style.
20th century music is a series of "isms" and "neo-isms." The primal energy
of Stravinsky's Rite of Spring has been called neo-Primitivism. The
intensely emotional tone of Schönberg's early music has been labeled
Expressionism. The return to clearly structured forms and textures has
been dubbed neo-Classicism. These terms have been employed in an
attempt to organize the diversity of styles running through the 20th
century.
Nationalism continued to be a strong musical influence in the first half of
the century. The study of folk songs enriched the music of numerous
composers, such as Ralph Vaughan Williams (England), Bela Bartok
(Hungary), Heitor Villa Lobos (Brazil) and Aaron Copland (USA). Jazz
and popular musical styles have also been tremendously influential on
"classical" composers from both the United States and Europe.
Technology has played a increasingly important role in the development of
20th century music. Composers have used recording tape as a
compositional tool (such as Steve Reich's Violin Phase). Electronically
generated sounds have been used both on their own and in combination
with traditional instruments. More recently, computer technology has been
used in a variety of ways, including manipulating the performance of
instruments in real time.

Medieval

When we explore Medieval music, we are dealing with the longest and most distant period of musical history. Saint Gregory is credited with organizing the huge repertory of chant that developed during the first centuries of the Christian church, hence the term Gregorian chant. He was pope from 590 to 604, and the Medieval era continued into the 1400s, so this period consists of almost a millennium's worth of music.
One of the principal difficulties in studying Medieval music is that a system for notating music developed only gradually. The first examples of musical notation date from around 900. For several centuries, notation only indicated what pitch (or note) to sing. The system for notating rhythm started in the 12th or 13th century.
Gregorian chant is monophonic, meaning music that consists of only one melodic line without accompaniment. The beauty of chant lies in the serene, undulating shapes of its melody. We do not know who wrote the melodies of Gregorian chant. Like folk melodies, the music probably mutated as it was passed down through generations and eventually reached its notated form.
Polyphony, music where two or more melodic lines are heard simultaneously, did not exist (or was not notated) until the 11th century. Unlike chant, polyphony required the participation of a composer to combine the melodic lines in a pleasing manner. Although most Medieval polyphonic music is anonymous--the names of the composers were either lost or never written down at all--there are composers whose work was so important that their names were preserved along with their music.

Renaissance Period 1400-1600 A.D.

In the mid-1500s, a prominent bishop commented that music composed
for the church should reflect the meaning of the words so that the listeners
would be moved to piety. This concept seems like a no-brainer today,
but it was a fairly new idea at the time. To suggest that Medieval
composers had no desire to write "expressive" music would be unfair.
But, it was the rediscovery of ancient Greek ideals in the Renaissance that
inspired many musicians to explore the eloquent possibilities of their art.
The increased value of individualism in the Renaissance is reflected by the
changing role of the composer in society. Unlike most of their Medieval
predecessors, the great masters of the Renaissance were revered in their
own lifetimes. The technique of printing music, while slow to evolve,
helped in the preservation and distribution of music and musical ideas.
Sacred music was still predominant, though secular music became more
prevalent and more sophisticated. The repertory of instrumental music
also began to expand significantly. New instruments were invented,
including the clavichord and virginal (both keyboard instruments) and
many existing instruments were improved.
Masses and motets were the primary forms of sacred vocal polyphony.
Secular vocal forms included motets, madrigals and songs (generally
accompanied by lute or a small instrumental ensemble or "consort").
Instrumental pieces were usually short polyphonic works or music for
dancing.
Compared with the Medieval style, Renaissance polyphony was lush and
sonorous. The era between Josquin Desprez and Palestrina is known as
"the golden age of polyphony." Imitation--where one melodic line shares,
or imitates the same musical theme as a previous melodic line--became an
important polyphonic technique. Imitation was one method composers
used to make complex music more easily comprehensible and give the
listener a sense of structure. Imitative polyphony can be heard in the
masses and motets of composers from Josquin onward and is featured in
instrumental music by Byrd, Gibbons, and the Gabriellis.