In Lenz's work, the first period opens with Beethoven's Trio set, Opus 1 and culminates with the performances in 1800 of his first symphony and Septet. The second period spans the period from the publication of his Moonlight Sonata to the Piano Sonata in E minor, Op. 90 in 1814. The last period covers Beethoven's mature works to his death in 1827. Although later scholars have called into question such a simplistic categorisation, it is still widely used. Extensive subsequent analytical consideration of Lenz's thesis has resulted in a slight revision of his original dates and broad consensus regarding Beethoven's three periods is as follows: a formative period that extends to 1802 a middle period from 1802 to 1814 a mature period from 1814 to 1827 Generally, each period demonstrates characteristic stylistic evolutions in Beethoven's musical language and preoccupations as well as important developments in the composer's personal life. Early period Many of Beethoven's early works were not assigned an opus number and were simply listed with the label WoO, which is the abbreviation for the German term "without opus number." Some, however, were published with opus numbers later on such as several compositions in the Eight Songs, op. 52. Although these were compiled between 1803 and 1805 and published in the latter year, were written during his early years in Vienna and Bonn. The compositions that Beethoven wrote in his formative period can be generally characterized by the composer's efforts to master the predominant classical language of the period. His works from this period can be subdivided into two, based on the composer's residence. First, various juvenalia, written when the adolescent Beethoven was in residence in Bonn and heavily indebted to the works of contemporaries, especially Mozart and his teacher, Christian Gottlob Neefe. These early efforts can be seen in a set of three piano sonatas and piano quartets (WoO 36) that Beethoven wrote before 1792. The Quartets, for instance, are each specifically modelled after three Violin sonatas Mozart published in 1781 – K 296, 379 and 380 – and Beethoven would later draw upon this familiarity in the composition of several of his own Violin Sonatas. Second, a number of more substantial and original works were written after Beethoven moved to Vienna and commenced studies with the famed Austrian composer and leading musical figure of the period, Joseph Haydn. As the 1790s progressed, his mastery of the Viennese