The concertos are… a happy medium between what is too easy and too difficult. They are very brilliant and pleasing to the ear, but naturally without being vapid. There are passages here and there which only connoisseurs can appreciate, yet the less learned cannot fail to be pleased, without knowing why.
Wolfgang Amadeus Mozart formulated his understanding of the concerto in a letter from Vienna sent to his father on December 28th, 1782. By then he had composed about 20 concertos for various solo instruments and orchestra. In total Mozart wrote nearly fifty concertos, a figure that matches the number of symphonies. He began his mastery of the genre by reworking keyboard sonatas by other composers (KV 37, 39–41) in 1767, after returning to Salzburg from a three-year grand tour of European countries. His last concerto was KV 622 for clarinet and orchestra, which was completed in October 1791 just two months before his death.