Did Beethoven really compose while completely deaf?
Yes — though the popular image of a man who heard nothing at all for his entire career compresses a gradual decline over some twenty-five years into a single dramatic fact.
What the evidence shows. Beethoven first complained of hearing trouble in his late twenties, describing a buzzing in his ears and difficulty with high notes and speech. In the Heiligenstadt Testament of 1802 — a despairing letter to his brothers that he never sent — he wrote about his isolation and his reluctance to admit the condition, which he had been concealing from all but close friends.
The decline was slow and uneven. He continued to perform publicly into his early forties, and his conversation books — notebooks visitors used to write down their side of a discussion — begin around 1818, indicating that speech had become largely inaccessible by then. By the premiere of the Ninth Symphony in 1824 he was profoundly deaf; the widely repeated account of him having to be turned around to see the applause he could not hear comes from witnesses and is plausible in substance.
How composition was still possible. This is the part people find hardest and it is the least mysterious. Trained musicians hear music internally. Any competent composer can read a score and perceive it without sound, much as a fluent reader hears a sentence without speaking it. Beethoven had decades of performing experience to draw on, and he continued to use a piano — reports of him sawing legs off an instrument to feel vibrations through the floor are more anecdote than documentation.
What the cause was remains unsettled. Proposed explanations include otosclerosis, lead poisoning, autoimmune disease and typhus. Analyses of hair and bone attributed to him have found elevated lead, though the provenance of some samples has been questioned, and a 2023 genomic study found no clear answer while identifying risk factors for liver disease.
What it did change was his life rather than his capability: the late quartets and the Ninth were written in deafness, and are not lesser works.