This exquisitely curated program is like a conversation with modernism. What does ‘modern’ music sound like? What makes it sound ‘modern’? How widely did its influence reach across the planet? At the head of the table is Debussy, and 13 of his keyboard preludes. You can hear the world of music breaking free of Romantic tradition in these pieces, as Debussy evokes sensations (The Sounds and Fragrances Swirl Through the Evening Air) and objects (Dead Leaves) with a glowing sonority that acted like a beacon to composers who followed: this is music both hazy and precise, mysterious and explicit.  Succeeding generations would take Debussy’s ability to evoke a vivid moment (or a remembrance of one) even further. In his very first piece, composed while Debussy was at work on his second book of Preludes, the 15-year-old Henry Cowell uses polytonality and clusters of chords to evoke the legendary Irish god of…