In the early 1960s, luthier José Ramírez III considered adding sympathetic strings to the classical guitar. He sought advice from the leading classical guitarists of the time, notably Andrés Segovia and Narciso Yepes, both of them players of Ramírez six-string guitars. Eventually they came up with a ten-string guitar. In Ser Instrumento, Yepes mentions that the reasons that led him to carry out the "design", of his instrument were acoustical/physical and musical. After some "initial protest" that the 10-string guitar envisioned by Yepes was "impossible" to construct, Ramírez agreed to the commission and completed the first of these instruments in March 1964. Yepes hastens to point out that he invented nothing Yepes recalled that after receiving his first ten-string guitar in 1964, he held a private concert for "friends, musicians, conductors and composers to listen to my instruments and then let them decide which is the better instrument for my concert. I can honestly say that during the concert I played the same compositions once on the six-string guitar and once on the ten-string guitar. They all preferred the ten-string guitar." Yepes then sought the opinion of his former teacher, Nadia Boulanger. After playing the ten-string guitar for her, Yepes recalled that, "She noticed that my playing on my new guitar had more resonance, and this is important, she noticed that I could stop the resonance with my hands if I wanted to. She also preferred my ten-string guitar." Segovia, though, was highly critical of Yepes's innovation, writing in 1974 that, "I absolutely do not believe that the guitar requires additional strings, neither at the right nor at the left of its fingerboard... the six it traditionally possesses are quite sufficient. The inventors of this futile addition in sonority are far from having exhausted the natural resources of the instrument." However, the validity of Segovia's criticism can be called into question: Firstly, Segovia seems to have been ignorant of the predominance of 'multi-string' guitars in the 19th Century, including the 21-stringed harpolyre for which Fernando Sor composed, as is evidenced in his claim that "Sor....did not feel a need for additional strings". Secondly, Segovia incorrectly claims that Yepes "added four thick tongues" to the guitar. In fact, Yepes added one "thick" string only. As Yepes pointed out, the first criticism from Segovia already came "before he had seen or even heard the instrument, soon after Ramírez made the ten-string guitar." Lastly, the questionable nature of Segovia's criticisms of the Yepes ten-string guitar are revealed by the fact that Segovia wrote "frequent letters" to José Ramírez III in which his unhappiness with weak "notes were always mentioned." Segovia complained that he "had to substitute or cancel a specific musical piece from one of his programs because the note that he had to emphasize coincided with one of the mortifying notes". Before the Yepes ten-string guitar was designed to address exactly this problem, Segovia had already complained to Ramírez III about how certain notes on the first string of his six-string guitar did "not have the same intensity as the others."
