How did Beethoven complete his 9th symphony while deaf?

Ludwig van Beethoven did not compose his entire 9th symphony while he was deaf. Although Beethoven started losing his hearing in the late 1790s, his symptoms worsened, and he was almost entirely deaf by 1818, several years before he started composing his 9th Symphony.

During the premiere of his 9th Symphony in Vienna in 1824, when the piece reached its end, the wildly cheering and applauding audience gave him a standing ovation. Since Beethoven could not hear the applause, the soprano soloist, Caroline Unger, turned him around to face the audience so he could see their enthusiastic response.