Bernstein could be so hyperbolic! I'm wondering how Tristan could be the central work in all of music history, when the composers that are most universally agreed upon as the greatest all came before Wagner? Even if Tristan was the sole influence and gateway to all of modernism (which it clearly is not), that statement would still be highly exaggerated.
I think Bernstein was all around a fantastic musician and educator, he just got carried away sometimes in his enthusiasm, he has made similarly exaggerated claims about Beethoven and about Stravinsky's Rite of Spring.
Granting that Bernstein had biases (like all of us) and was a bit of a drama queen, he has a point. It isn't necessary to accept that any single work is "central" to Western music, but if we do entertain that as a reasonable notion it's hard to think of another work that qualifies as well as
Tristan und Isolde. And I think it qualifies on grounds both musical and cultural.
Tristan came in the very middle of the 19th century, a moment when the basic harmonic language of Western music had congealed at the hands of the Classical masters and was in the process of being expanded in ways that existing theoretical concepts could describe only with difficulty, if at all. More fundamentally, it came at the time when the very idea of music - or, to be precise, the idea of musical meaning and expression - had been transformed by the Romantic movement from a representation of ideal values and affective categories to a seismograph of the soul, psyche, or inner life of the individual. It was an enormous expansion of the notion of what music could or should concern itself with, and the elements of music - melody, harmony, form - had to find radically new shapes in order to represent philosophical concepts, poetic ideas, phenomena of nature, and the infinite nuances of human feeling.
Wagner was ideally suited to play a major role in this evolution. Having grown up around the theater where his stepfather was a performer, and having written plays as a child before he composed music, he was essentially a musical dramatist, and his works were eventually to prove that no art form is more sympathetic to Romanticism's expressive premises and expanded musical techniques than opera. It was the dramatist in Wagner that provided the impetus for his musical innovations - his expansion of harmony and orchestration, his use of pregnant and adaptable motifs to weave rich and extended textures and create a psychological narrative, and his breakup of traditional forms. And it was the quintessentially Romantic theme of
Tristan in particular - romantic love, or erotic passion - that forced these tendencies to extremes that sent shock waves through the musical - and nonmusical - culture of Europe.
A three-hour opera almost devoid of physical action and devoted almost entirely to the uninhibited probing of a central focus of the subjective life of the human individual was something that couldn't have been attempted, or probably even imagined, before its own particular moment in history. It can be seen in retrospect as the work that Wagner was destined to write, and the writing of it had for him the quality of a compulsion and a revelation, stretching his musical powers so far beyond his own previous efforts that he himself found the work's emergence from his psyche astonishing and almost frightening. But it can just as well be seen as the work which Romanticism itself was striving to compose, the climactic product of a new sensibility which had revolutionized Western society as the focus of human perception and purpose shifted from God and society to the human individual. In its intense exploration of passion,
Tristan, based on the classic romance of the Middle Ages, locates passion - in its dual sense of love and suffering - at the center of the emotional life of Western man, and it's a work that continues, like passion itself, to be as unsettling as it is exalting.
Few composers could escape completely from the grip of this work on the musical thinking and feeling of the decades that followed it. I think an exhaustive tracing of its influence would show Bernstein's sense of its importance to be pretty accurate.