How did Domenico Scarlatti expand binary form in his sonatas?

Domenico Scarlatti significantly expanded the traditional binary form—a structure typically consisting of two complementary sections—through several key innovations in his keyboard sonatas.

His approach to expanding this form included:

• Thematic Differentiation: Unlike many of his contemporaries who relied on closely linked melodic-rhythmic materials, Scarlatti often differentiated between two contrasting thematic ideas within the first section of his sonatas.12
• Rounded Binary Structure: Many of his works utilize a "rounded" binary form, where the second section returns relatively quickly to both the original key and the melodic-rhythmic features of substantial portions of the first section. This organization effectively approximates the ternary outline that became prevalent in later 18th- and 19th-century compositions.1
• Harmonic and Technical Complexity: Scarlatti extended the tonal range of his pieces and incorporated audacious dissonances, unconventional voice leading, and far-flung modulations. These harmonic developments were paired with spectacular innovations in keyboard virtuosity, such as hand crossing, which elevated the expressive potential of the harpsichord.3

Through these methods, Scarlatti transformed simple dance-based binary structures into a sophisticated musical language that anticipated stylistic features found in the works of later composers like Haydn and Mozart.34