It was in Haydn's hands that the keyboard sonata developed from a simple drawing-room divertimento to the level of a high art-form and the greatest among his sonatas have an intellectual rigour and a dramatic sweep that were rarely equalled by Mozart, and not surpassed until Beethoven revolutionized the form in the closing years of the eighteenth century. His earliest sonatas were composed with the harpsichord in mind, but in later years he began increasingly to exploit dynamic contrasts of a kind that could only be obtained on the fortepiano.