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The Enlightenment's simplicity and focus on naturalistic expression began to be expressed in opera. Gluck, a prominent classical-era opera reformer, was inspired by Algarotti's Essay on the Opera (1755).

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The development of classical form (late 18th century) 

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The development of classical form (late 18th century) 

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The late 18th century is where classical form became fully developed. A form such as the sonata was not seen as a formula, but rather the interplay between harmony and themes.

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Music publishing and the lied (general 18th century)

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Music publishing and the lied (general 18th century)

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Music publishing became a source of income for composers as the market began to expand. This is how C.P.E. Bach achieved financial security.

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Musicians under patronage (general 18th century)

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Musicians under patronage (general 18th century)

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As musical patronage gained traction, musicians across Europe were provided with security. Although, musicians were now viewed as household servants.

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Tonal harmony had already been developing, but this treatise is what formally established tonal theories and functions. It viewed chords in a new way, as triads, regardless of the bass note.

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(Martines) Sonata in A Major, IMM 14 (1765)

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(Martines) Sonata in A Major, IMM 14 (1765)

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It is easy to hear the similar character between Martines and Haydn in the first movement. This sonata is one of only few Martines works to be available through a publisher.

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(Scarlatti) Sonata in G minor, K. 426 (post-1735)

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(Scarlatti) Sonata in G minor, K. 426 (post-1735)

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Scarlatti wrote a lot of keyboard sonatas. They are also challenging to assign dates to. I selected this piece because it is a plain sonata, representative of the bulk of his work.

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(Haydn) String Quartet in G Major, Op. 76, No. 1 (ca. 1797)

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(Haydn) String Quartet in G Major, Op. 76, No. 1 (ca. 1797)

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Haydn was also considered to be the father of the classical string quartet. This is a later Haydn work, and it follows the typical four-movement form plan for string quartets.

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A classical-era female composer, Marianna Martines was gifted and worked with Haydn. Unfortunately, her works became obscure following her passing. Only recently have they been rediscovered.

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(Mozart) Symphony No. 40 in G minor, K. 550 (1788)

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(Mozart) Symphony No. 40 in G minor, K. 550 (1788)

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A later work of Mozart, sometimes referred to as "The Great G minor Symphony" is right behind his last symphony (Jupiter). The piece showcases Mozart's refined classical craft after his years of composing and innovating.

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(Sammartini) Symphony in C Major, J-C 4 (ca. 1750)

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(Sammartini) Symphony in C Major, J-C 4 (ca. 1750)

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Sammartini is known for his symphonies, which advanced the classical world's symphonic works. The first movement is in sonata form.

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(C.P.E. Bach) Wurttemberg Sonata No. 1 in A minor, H. 30 (1742)

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(C.P.E. Bach) Wurttemberg Sonata No. 1 in A minor, H. 30 (1742)

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This piece is representative of the material C.P.E. Bach would compose for amateurs to play. It is significant in regards to being a usual composition of C.P.E. Bach.

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Mozart, who also happened to be connected with Haydn, also composed under many different classical-era genres, further progressing the era as a whole. His style was very uniform and he was very proficient.

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Haydn is known as the "father of the symphony," and his career consisted of innovations and evolution in the Classical style. He helped develop quartets, sonatas, especially symphonies, and more.

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A child of Johann Sebastian Bach, C.P.E. Bach wrote keyboard sonatas for amateurs to play, bringing him great success. He was also a leader in empfindsamkeit.

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Sammartini was a very significant early symphony composer. He helped lay the groundwork for symphonies for late-classical composers.

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Scarlatti is known for his 555 sonatas (for harpsichord). He composed these from the early 18th century to his death. These compositions helped establish the sonata.