A trained or otherwise skilled composer can hear music in their mind by reading the score (and while he wrote it). For sure, Beethoven knew how powerful his mus

A trained or otherwise skilled composer can hear music in their mind by reading the score (and while he wrote it). For sure, Beethoven knew how powerful his music was. He also intimately knew theory and how music 'worked' and aside from inventing a great number of things in music, he applied theory expertly. Modern day composers in the conservatory track are expected to have the same set of skills. A trained conductor can do the same.