On 2 August 1788 Mozart wrote a letter to his sister Nannerl. She was living in Salzburg. He had sent her some pieces for the piano. He wrote, "Indeed you have every reason to be vexed with me! But will you really be so, when you receive by this mail coach my very latest compositions for the keyboard? Surely not! This, I hope, will make everything all right again." This passage might refer to the Sonata in C. But it may refer to other keyboard compositions Mozart wrote the same year. 