First Movement: Caminhando (Allegretto)

Second Movement: Sonhando (Poco lento)

Third Movement: Brincando (Mesto)

Composed in 1958, this small sonata was commissioned by an amateur fortepiano enthusiast and inspired by Haydn's style. The commissioner passed away after its completion. Five years after its composition, the same movements were once performed as the second and third movements of Piano Sonata No. 4. However, Williamson considered this work unsuitable for contemporary grand pianos and left it buried among his unpublished works. Thirty years later, the work was revived with the assistance of Australian pianist Antony Gray, from Victoria. Williamson himself gave the complete premiere at the University of Melbourne in 1993.

Reflecting its original intended use for the fortepiano, its musical character is entirely different from his First and Second Sonatas. It is lovely and lyrical, yet possesses a witty atmosphere with a sense of floating lightness. The final movement is a set of variations. The theme is an extremely simple melody of only seven notes, but the variations are light and full of movement. The final variation is a chorale, bringing the entire work to a gentle and reflective close.