There is considerable debate amongst scholars as to whether the birth of the viola preceded or succeeded that of the violin. However, iconographic and documentary evidence indicate that the violin, viola, and cello most likely evolved together as a family of instruments very early in the sixteenth century and almost certainly in northern Italy. Part-writing for the viola in chamber music has changed dramatically over time. By the end of the seventeenth century, while the violin had remained popular in chamber music, the viola was very much neglected.
It was not until the end of the eighteenth century, when Mozart and Beethoven promoted the viola to a position of equality with the second violin and the cello in the string quartet, that the viola was given more interesting soloistic part-writing to play. The question then is: why did the viola fall out of favor in chamber music from the time period following its birth to the end of the seventeenth century? At the end of the sixteenth century, the viola was deemed the instrument of the middle, being used for both the alto and tenor registers.
In five-part ensemble writing, three violas were used for the inner voices. However, after 1600, when part-writing changed from five-part to four-part harmony, essentially eliminating one of the viola’s lines, violas gradually fell out of demand. The emergence of the trio sonata as the most popular form of chamber music in the seventeenth century excluded the viola completely, as it generally featured two violins and continuo.
In his book, The History of the Viola, Riley states: The omission of the viola from the trio sonata was an unfortunate development that retarded the progress of this instrument in many ways. Not only was the viola usually excluded from the most popular and most prevalent form of instrumental chamber music of the Baroque era, but also composers were failing to recognize it as a solo instrument.  From this time to approximately 1740, the viola held a minor, even insignificant role in part-writing, playing only harmonic filler while the violin was given the main melodies.
The end of the eighteenth century marked a change in the treatment of the viola in chamber music. The change “came about partly because a basic concept of late eighteenth century chamber music was that a single player played each part (thus setting chamber music apart from the orchestra where each string part . . . was played by several players). ” A greater equality of part writing can be observed in the mature chamber music, especially string quartets, of Mozart and Beethoven. In Mozart’s last string quartet (K. 90, 1790), the part writing is equalized, and solos are given to the viola, with a considerable degree of virtuosity demanded of the instrument. In the passage below, the first violin states the melody and then two bars later the viola plays the same passage just an octave lower. Example 1. Wolfgang Amadeus Mozart, String Quartet no. 23, k. 590, 1st Movement, mm. 51-54 [pic] This example clearly demonstrates equal part-writing for the viola with that of the violin or the other instruments.
In conclusion, it is difficult to answer the question as to why the viola fell out of favor in chamber music from the time period following its birth in the early sixteenth century to the end of the seventeenth century. One possible reason is that no parts of importance were written for it because there were no good viola players during the formative period of the instrument. This is supported by the general sentiment in the music community that good viola players have always been scarce, and therefore in the early days of the quartet they must have been practically non-existent.
Another possible reason, which is better supported, is that the viola lost favor because no parts of importance were written for it. Probably one of the chief factors in the viola’s advancement was the composer’s personal interest to take part in concerted music. Since composers did not want to spend much time learning the technique of a demanding instrument, they took up the viola. Therefore, it can be easily understood how the affection felt by a composer for his own instrument was reflected in the viola’s growing importance in chamber music.
Clarke, Rebecca. “The History of the Viola in Quartet Writing. ” Music ; Letters 4, no. 1 (1923): 6-17. Boyden, David D. , and Ann M. Woodward. “Viola. ” In Grove Music Online. Oxford Music Online, http://www. oxfordmusiconline. com/subscriber/article/grove/ music/29438. Froggatt, Arthur. “The Viola. ” The Musical Times 51, no. 812 (1910): 638-40. Harvey, Brian. The Violin Family and Its Makers in the British Isles. New York: Oxford University Press, 1995. Montagu, Jeremy. “Viola. In The Oxford Companion to Music, edited by Alison Latham. Oxford Music Online, http://www. oxfordmusiconline. com/subscriber/ article/opr/t114/e7157. Nelson, Sheila. The Violin and Viola. New York: W. W. Norton, 1972. ——–. The Violin Family. London: C. Tinling, 1964. Riley, Maurice. The History of the Viola. Ann Arbor, MI: Braun-Brumfield, 1980. Sandys, William, and Simon Andrew Forster. History of the Violin. Mineola, NY: Dover Publications, 2006. Watson, Arthur. “Mozart and the Viola. ” Music & Letters 22, no. 1 (1941): 41-53.