Two Young Girls at the Piano (1892)
Pierre-Auguste Renoir, CC0, via Wikimedia Commons

In 1700, an Italian instrument maker named Bartolomeo Cristofori created an improvement to the harpsichord. Instead of a traditional harpsichord, in which the keyboard controls a mechanism that plucks the strings, Cristofori's instrument stuck the strings with a small, felt-tipped mallet. This allowed the player to control the volume of the instrument based on how hard or soft he hit the keys. Because of its dynamic capabilities, Cristofori called his instrument the piano-forte, later shortened to the piano.

The piano soon became one of the most popular European instruments. A new genre developed called the sonata, a variation of the concerto where a solo instrument is accompanied by a piano rather than a full orchestra. A work for solo piano is also called a sonata.

Like the concerto, sonatas generally took a three-movement fast/slow/fast form, with the first movement in sonata-allegro form, a combination of a ternary form with a double variation. The second movement would usually be at a slower adagio tempo, while the third often would be in a rondo form.

• Introduction
• Exposition
  • Theme A (tonic key)
  • Transition
  • Theme B (dominant or relative major)
• Development
  • The composer does variations on one or both themes, ending by pedaling the dominant.
• Recapitulation
  • Theme A (tonic key)
  • Transition to Coda
  • Theme B (tonic key)

A very common accompaniment texture used in the Classical Period was known as Alberti bass. This technique begins with a chord progression like the one below.

To create an Alberti bass, the triads are simply broken up into a "low → high → middle → high" pattern.

Note that this does not always mean "root → fifth → third → fifth." It depends on the inversion.