Why were many of Domenico Scarlatti’s sonatas composed in pairs?

At least 388 of Domenico Scarlatti’s 555 keyboard sonatas were composed as pairs, effectively functioning as two-movement sonatas.1

These pairings were designed to serve specific musical purposes, including:

• Contrasting movements: Pairing slow movements with fast ones.1
• Complementary structures: Coupling two fast movements together.1
• Tonal expansion: Extending the total tonal range of the work by conceiving the pair as a single, unified musical unit.1

While these works are often performed as individual pieces today, they were frequently designed to be played in pairs or, in some cases, in triptychs (groups of three). Modern editions, such as those by Ralph Kirkpatrick and Kenneth Gilbert, maintain these original pairwise arrangements to preserve the intended coherence of Scarlatti's compositions.12