The historical and clinical consensus, based on the available evidence from Beethoven’s own descriptions and from the autopsy findings, has generally pointed toward a combination of factors. Otosclerosis—a condition involving abnormal bone growth in the middle ear that progressively impairs the conduction of sound—has been proposed as one possible contributor. The autopsy found what Johann Wagner described as unusual features of the auditory nerves and surrounding tissue, though the interpretation of these findings has varied across different medical historians and clinicians who have reviewed them.
Some researchers have proposed that an episode of typhus or another febrile illness in Beethoven’s early adulthood may have contributed to nerve damage in his auditory system. Others have pointed to the possibility of Paget’s disease, an autoimmune inner ear condition, or to acoustic trauma from exposure to loud sounds during performances. None of these proposals has achieved consensus status in the literature.
What the conversation books document, for the final decade of Beethoven’s life, is a person who had adapted functionally to complete deafness. He composed. He continued to receive visitors and engage in wide-ranging discussions. He worked on revision and publication of earlier works. He followed political and cultural news. He had opinions about what was happening in Vienna’s musical world even though he could no longer participate in it as a performer. His deafness had removed him from performing but had not removed him from music.
The late works—the last five string quartets, the Missa Solemnis, the Ninth Symphony, the Diabelli Variations—were composed by a deaf man working entirely from internalized musical experience. This is a documented fact. What it meant for the character of the music—whether the inaccessibility of external sound produced a more internal, abstract quality in the compositions—remains a matter of musicological interpretation rather than established fact.