In the middle of the 18th century, Europe began to move toward a new style in architecture, literature, and the arts, generally known as Classicism. This style sought to emulate the ideals of Classical antiquity, especially those of Classical Greece. While still tightly linked to court culture and absolutism, with its formality and emphasis on order and hierarchy, the new style was also "cleaner". It favored clearer divisions between parts, brighter contrasts and colors, and simplicity rather than complexity. In addition, the typical size of orchestras began to increase.
The remarkable development of ideas in "natural philosophy" had already established itself in the public consciousness. In particular, Newton's physics was taken as a paradigm: structures should be well-founded in axioms and be both well-articulated and orderly. This taste for structural clarity began to affect music, which moved away from the layered polyphony of the Baroque period toward a style known as homophony, in which the melody is played over a subordinate harmony. This move meant that chords became a much more prevalent feature of music, even if they interrupted the melodic smoothness of a single part. As a result, the tonal structure of a piece of music became more audible.
The new style was also encouraged by changes in the economic order and social structure. As the 18th century progressed, the nobility became the primary patrons of instrumental music, while public taste increasingly preferred comic opera. This led to changes in the way music was performed, the most crucial of which was the move to standard instrumental groups and the reduction in the importance of the —the rhythmic and harmonic ground of a piece of music, typically played by a keyboard (harpsichord or organ) and potentially by several other instruments. One way to trace the decline of the continuo and its figured chords is to examine the disappearance of the term, meaning a mandatory instrumental part in a work of chamber music. In Baroque compositions, additional instruments could be added to the continuo according to preference; in Classical compositions, all parts were specifically noted, though not always notated, so the term "obbligato" became redundant. By 1800, it was practically extinct.
Economic changes also had the effect of altering the balance of availability and quality of musicians. While in the late Baroque a major composer would have the entire musical resources of a town to draw on, the forces available at a hunting lodge were smaller and more fixed in their level of ability. This was a spur to having primarily simple parts to play, and in the case of a resident virtuoso group, a spur to writing spectacular, idiomatic parts for certain instruments, as in the case of the Mannheim orchestra. In addition, the appetite for a continual supply of new music, carried over from the Baroque, meant that works had to be performable with, at best, one rehearsal. Indeed, even after 1790 Mozart writes about "the rehearsal", with the implication that his concerts would have only one.
I am taking classical music. An aria is simply a female solo with an orchestra. a requiem is a song for the dead, not sad music. there are different kinds, the chants of the middle ages are called gregorian chants. there is secular and non ecular music it depends on what kind you are looking for, there are differet time periods.